CHEMICAL ENGINEERING - Chemical engineering sits at the nexus between science and technology. It's one of the major engineering disciplines. Chemical engineering is applied chemistry. It is the branch of engineering concerned with the design, construction, and operation of machines and plants that perform chemical reactions to solve practical problems or make useful products. It starts in the lab, much like science, yet progresses through the design and implementation of a full-scale process, its maintenance, and methods of testing and improving it. Chemical engineers use math, physics, and economics to solve technical problems. Chemical engineers apply knowledge of chemistry in addition to other engineering disciplines. Chemical engineers sometimes are called 'universal engineers' because their scientific and technical mastery is so broad. You could consider a chemical engineer to be a type of engineer who knows a lot of science. Another perspective is that a chemical engineer is a practical chemist. Some chemical engineers make designs and invent new processes. Some construct instruments and facilities. Some plan and operate facilities. Chemical engineers also make chemicals. Chemical engineers have helped develop atomic science, polymers, paper, dyes, drugs, plastics, fertilizers, foods, petrochemicals, pretty much everything you can imagine. They devise ways to make products from raw materials and ways to convert one material into another useful form.

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Chemical Engineering

What Is Chemical Engineering?

By Anne Marie Helmenstine, Ph.D.

Chemical engineering sits at the nexus between science and technology. It's one of the major engineering disciplines.

Take a look at what exactly chemical engineering is, what chemical engineers do, and how to become a chemical engineer.

What Is Chemical Engineering?

Chemical engineering is applied chemistry. It is the branch of engineering concerned with the design, construction, and operation of machines and plants that perform chemical reactions to solve practical problems or make useful products.

It starts in the lab, much like science, yet progresses through the design and implementation of a full-scale process, its maintenance, and methods of testing and improving it.

What Is a Chemical Engineer?

Like all engineers, chemical engineers use math, physics, and economics to solve technical problems.

The difference between chemical engineers and other types of engineers is that they apply knowledge of chemistry in addition to other engineering disciplines.

Chemical engineers sometimes are called 'universal engineers' because their scientific and technical mastery is so broad.

You could consider a chemical engineer to be a type of engineer who knows a lot of science.

Another perspective is that a chemical engineer is a practical chemist.

What Do Chemical Engineers Do?

Some chemical engineers make designs and invent new processes.

Some construct instruments and facilities. Some plan and operate facilities.

Chemical engineers also make chemicals.

Chemical engineers have helped develop atomic science, polymers, paper, dyes, drugs, plastics, fertilizers, foods, petrochemicals, pretty much everything you can imagine.

They devise ways to make products from raw materials and ways to convert one material into another useful form.

Chemical engineers can make processes more cost-effective or more environmentally friendly or more efficient.

Chemical engineers also teach, work with the law, write, create new companies, and perform research.

As you can see, a chemical engineer can find a niche in any scientific or engineering field.

While the engineer often works in a plant or lab, she's also found in the boardroom, office, classroom, and out at field locations.

Chemical engineers are in high demand, so they typically command higher salaries than chemists or other types of engineers.

What Skills Does a Chemical Engineer Need?

Chemical engineers work in teams, so an engineer needs to be able to work and communicate with others.

Chemical engineers study mathematics, energy and mass transfer, thermodynamics, fluid mechanics, separation technology, matter and energy balances, and other topics of engineering, plus they study chemical reaction kinetics, process design, and reactor design.

A chemical engineer needs to be analytical and meticulous.

Someone who is great at chemistry and math and loves solving problems would enjoy the discipline.

Typically, chemical engineering progresses to a masters degree because there's so much to learn.

More About Chemical Engineering

If you'd like to learn more about chemical engineering, start with reasons to study it.

View the chemical engineer job profile and learn how much money an engineer makes. There's also a handy list of types of jobs in chemical engineering.

Anne Marie Helmenstine, Ph.D.

Chemistry Expert

Education

Ph.D., Biomedical Sciences, University of Tennessee at Knoxville

B.A., Physics and Mathematics, Hastings College

Introduction

Ph.D. in biomedical sciences from the University of Tennessee at Knoxville - Oak Ridge National Laboratory.

Science educator with experience teaching chemistry, biology, astronomy, and physics at the high school, college, and graduate levels.

ThoughtCo and About Education chemistry expert since 2001.

Widely-published graphic artist, responsible for printable periodic tables and other illustrations used in science.

Experience

Anne Helmenstine, Ph.D. has covered chemistry for ThoughtCo and About Education since 2001, and other sciences since 2013. She taught chemistry, biology, astronomy, and physics at the high school, college, and graduate levels. She has worked as a research scientist and also abstracting and indexing diverse scientific literature for the Department of Energy.

In addition to her work as a science writer, Dr. Helmenstine currently serves as a scientific consultant, specializing in problems requiring an interdisciplinary approach. Previously, she worked as a research scientist and college professor. 

Education

Dr. Helmenstine holds a Ph.D. in biomedical sciences from the University of Tennessee at Knoxville and a B.A. in physics and mathematics with a minor in chemistry from Hastings College. In her doctoral work, Dr. Helmenstine developed ultra-sensitive chemical detection and medical diagnostic tests.

ThoughtCo and Dotdash

ThoughtCo is a premier reference site focusing on expert-created education content. We are one of the top-10 information sites in the world as rated by comScore, a leading Internet measurement company. Every month, more than 13 million readers seek answers to their questions on ThoughtCo.

For more than 20 years, Dotdash brands have been helping people find answers, solve problems, and get inspired. We are one of the top-20 largest content publishers on the Internet according to comScore, and reach more than 30% of the U.S. population monthly. Our brands collectively have won more than 20 industry awards in the last year alone, and recently Dotdash was named Publisher of the Year by Digiday, a leading industry publication.

https://www.thoughtco.com/what-is-chemical-engineering-606098 

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THE MAGIC OF A THERMOS - Why A Thermos Keep Things Cold Longer Than It Keeps Things Hot - A thermos appears to be more effective for keeping cold liquids chilled because the difference in temperature between the ambient temperature and perceived “cold” and “hot” liquids. Heat energy will transfer out of hot liquids more rapidly than it will transfer into cold liquids. Basically, whether you put steaming hot soup or ice-cold water in the thermos, the vacuum bubble surrounding the inner flask will keep the temperature stable for an extended period of time. Energy is created by the vibrational movement of atoms and molecules, and this energy can be transferred. When this transfer of energy occurs as a result of a temperature difference, it is called heat energy. In the case of differing temperatures, heat energy flows from a hot object to a cold object. A vacuum flask is able to prevent or minimize heat transfer between the exterior environment and the liquid inside the thermos. Heat transfer is how heat energy is transferred between objects, whether that is a convection stove boiling a pot of water, the sun heating the planet or a campfire warming a marshmallow! When it comes to the contents of a thermos and the exterior environment, heat transfer is significantly delayed by the vacuum layer.

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The Magic Of A Thermos

Why Does A Thermos Keep Things Cold Longer Than It Keeps Things Hot?

John Staughton 

A thermos appears to be more effective for keeping cold liquids chilled because the difference in temperature between the ambient temperature and perceived “cold” and “hot” liquids.

Heat energy will transfer out of hot liquids more rapidly than it will transfer into cold liquids.

Can you remember back to lunchtime during your school days?

For me, my lunch bag would contain a peanut butter and jelly sandwich, an apple, a bag of chips and a room temperature Capri Sun.

I still remember the envy I had for those kids who would pull out a thermos from their bag and begin slurping up warm soup or drinking ice-cold juice.

All of my food tended to be the same temperature, and my parents refused to buy me a thermos, insisting that I would lose it (they were probably right).

The apparent magic of a thermos has perplexed me for many years, but I have also learned an interesting fact from various thermos-loving friends.

In short, their thermoses are better at keeping cold liquids cold than they are at keeping hot liquids hot. Why is that?

What is a Thermos?

Before we can understand its intricacies, let’s take a broad look at thermoses to have a clearer idea of the subject.

A thermos is any container that is able to keep liquids either hot or cold, thanks to a double-walled design featuring a vacuum.

More formally known as a vacuum flask, this invention has been around since the end of the 19th century, when researcher Sir James Dewar stumbled upon it in the course of his study of cryogenics.

Dewar placed two brass flasks inside of one another, and joined them at the neck. The air that became trapped between the two flasks in a thermos can be removed or evacuated, creating a vacuum inside the space.

Without any air to facilitate heat transfer, liquid placed in the inner flask will be isolated from the exterior conditions, and will thus be able to retain its temperature more effectively.

Although this was a rudimentary version of a thermos, and only offered a partial vacuum, it was a huge breakthrough.

Basically, whether you put steaming hot soup or ice-cold water in the thermos, the vacuum bubble surrounding the inner flask will keep the temperature stable for an extended period of time.

The best thermoses on the market claim to keep items cold or hot for two days, and up to 10 days if the liquid is iced!

While thermos efficiency has certainly improved over the years, people still claim that liquids cool off before they warm up, a claim that is directly related to heat transfer.

Heat Transfer in a Thermos

Energy is created by the vibrational movement of atoms and molecules, and this energy can be transferred.

When this transfer of energy occurs as a result of a temperature difference, it is called heat energy. In the case of differing temperatures, heat energy flows from a hot object to a cold object.

As mentioned above, a vacuum flask is able to prevent or minimize heat transfer between the exterior environment and the liquid inside the thermos.

Why does this matter? Because heat transfer is a key part of thermal engineering and thermodynamics, and it occurs all across the universe!

Heat transfer is how heat energy is transferred between objects, whether that is a convection stove boiling a pot of water, the sun heating the planet or a campfire warming a marshmallow!

When it comes to the contents of a thermos and the exterior environment, heat transfer is significantly delayed by the vacuum layer.

If it was filled with hot soup, the heat energy from the interior flask would try to heat up the colder gas molecules in the space between, which could then pass that heat energy to the outer flask wall and the exterior environment temperature, which would be colder than the hot soup.

However, there is no gas in the vacuum space, so that transfer of heat energy does not readily occur.

Similarly, if the inner flask is filled with ice water, the warmth of the outer environment will warm the flask, but there are no air molecules to transfer that heat energy across to the inner flask wall, and thus the cold water stays cold!

So Why Are Thermoses Better At Keeping Things Cold?

Concerning heat transfer, the greater the difference in temperature between two objects, the faster the energy will transfer between them, from hot to cold.

Our perception of hot and cold is also an important thing to consider in this question.

Consider that room temperature is about 70 degrees Fahrenheit (21 Celsius); water freezes at 32 degrees Fahrenheit (0 Celsius) and boils at 212 degrees Fahrenheit (100 Celsius).

Thus, the difference between room temperature and a thermos of an ice-cold drink is much smaller than the difference between room temperature and a thermos of hot soup off the stove.

Now, a thermos is far from perfect, and some heat is gradually lost.

Every time you open the thermos, for example, a significant amount of heat transfer will occur (i.e., your coffee will cool or your water will warm).

However, a larger amount of energy will be transferred between coffee and the cooler air, due to the larger difference in temperature.

A smaller amount of energy will transfer between the cold water and the warmer air, due to their smaller difference in temperature.

This is where human perception comes into play; we will be more aware of the temperature change in the coffee than the temperature change in the water.

As a result, popular opinion states that thermoses are better at keeping things cold than keeping things warm, but by percentage of heat energy transferred, thermoses are equally efficient at either end of the temperature spectrum.

A Final Word

The reason that thermoses seem more effective at keeping things chilled than warm is our perception of the temperature change.

Hot liquids (i.e., coffee and soup) are prepared considerably hotter than room temperature, whereas a cold drink is much closer to room temperature.

As heat transfer occurs, we are simply more aware of the difference in heat energy as hot liquids change.

A good way to avoid disappointment is to consume the contents of your thermos immediately upon opening it for the very first time, before heat energy has a chance to make its moves!

John Staughton is a traveling writer, editor, publisher and photographer who earned his English and Integrative Biology degrees from the University of Illinois. He is the co-founder of a literary journal, Sheriff Nottingham, and the Content Director for Stain’d Arts, an arts nonprofit based in Denver. On a perpetual journey towards the idea of home, he uses words to educate, inspire, uplift and evolve.

https://www.scienceabc.com/eyeopeners/why-does-a-thermos-keep-things-cold-longer-than-it-keeps-things-hot.html

FIRST LAW OF THERMODYNAMICS - The first law of thermodynamics is also known as the law of conservation of energy, which states energy can transform from one form into another, but can neither be created nor destroyed within an isolated system. Perpetual motion machines of the first kind are impossible, according to the first law of thermodynamics. The states that the total energy of a system and its surroundings remain constant. In other words, it is not possible to construct an engine that will cycle and produce work continuously from nothing.

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First Law of Thermodynamics

Definition

Chemistry Glossary Definition of First Law of Thermodynamics

by Anne Marie Helmenstine, Ph.D. 

The first law of thermodynamics is the physical law which states that the total energy of a system and its surroundings remain constant.

The law is also known as the law of conservation of energy, which states energy can transform from one form into another, but can neither be created nor destroyed within an isolated system.

Perpetual motion machines of the first kind are impossible, according to the first law of thermodynamics.

In other words, it is not possible to construct an engine that will cycle and produce work continuously from nothing.

First Law of Thermodynamics Equation

The equation for the first law can be confusing because there are two different sign conventions in use.

In physics, particularly when discussing heat engines, the change in the energy of a system equals the heat flow in the system from the surroundings minus the work done by the system on the surroundings.

The equation for the law may be written:

ΔU = Q - W

Here, ΔU is the change in the internal energy of a closed system, Q is the heat supplied to the system, and W is the amount of work done by the system on the surroundings.

This version of the law follows the sign convention of Clausius.

However, the IUPAC uses the sign convention proposed by Max Planck. Here, net energy transfer to a system is positive and net energy transfer from a system are negative.

The equation then becomes:

ΔU = Q + W

The IUPAC is the International Union of Pure and Applied Chemistry. It is an international scientific organization, not affiliated with any government. The IUPAC strives to advance chemistry, in part by setting global standards for names, symbols, and units. Nearly 1200 chemists are involved in IUPAC projects. Eight standing committees oversee the Union's work in chemistry.

The Role of IUPAC

The IUPAC was formed in 1919 by scientists and academicians who recognized a need for standardization in chemistry. The predecessor of the IUPAC, the International Association of Chemical Societies (IACS), met in Paris in 1911 to propose issues that needed to be addressed. From the beginning, the organization has sought international cooperation between chemists. In addition to setting guidelines, the IUPAC sometimes helps to resolve disputes. An example is the decision to use the name 'sulfur' instead of both 'sulfur' and 'sulphur'.

Anne Marie Helmenstine, Ph.D.

Introduction

Ph.D. in biomedical sciences from the University of Tennessee at Knoxville - Oak Ridge National Laboratory.

Science educator with experience teaching chemistry, biology, astronomy, and physics at the high school, college, and graduate levels.

ThoughtCo and About Education chemistry expert since 2001.

Widely-published graphic artist, responsible for printable periodic tables and other illustrations used in science.

Experience

Anne Helmenstine, Ph.D. has covered chemistry for ThoughtCo and About Education since 2001, and other sciences since 2013. She taught chemistry, biology, astronomy, and physics at the high school, college, and graduate levels. She has worked as a research scientist and also abstracting and indexing diverse scientific literature for the Department of Energy.

In addition to her work as a science writer, Dr. Helmenstine currently serves as a scientific consultant, specializing in problems requiring an interdisciplinary approach. Previously, she worked as a research scientist and college professor. 

Education

Dr. Helmenstine holds a Ph.D. in biomedical sciences from the University of Tennessee at Knoxville and a B.A. in physics and mathematics with a minor in chemistry from Hastings College. In her doctoral work, Dr. Helmenstine developed ultra-sensitive chemical detection and medical diagnostic tests.

ThoughtCo and Dotdash

ThoughtCo is a premier reference site focusing on expert-created education content. We are one of the top-10 information sites in the world as rated by comScore, a leading Internet measurement company. Every month, more than 13 million readers seek answers to their questions on ThoughtCo.

For more than 20 years, Dotdash brands have been helping people find answers, solve problems, and get inspired. We are one of the top-20 largest content publishers on the Internet according to comScore, and reach more than 30% of the U.S. population monthly. Our brands collectively have won more than 20 industry awards in the last year alone, and recently Dotdash was named Publisher of the Year by Digiday, a leading industry publication.

https://www.thoughtco.com/first-law-of-thermodynamics-definition-604343

ENTHALPY DEFINITION IN CHEMISTRY AND PHYSICS - Enthalpy is the sum of the internal energy added to the product of the pressure and volume of the system. It reflects the capacity to do non-mechanical work and the capacity to release heat. Change in enthalpy is calculated rather than enthalpy, in part because total enthalpy of a system cannot be measured. However, it is possible to measure the difference in enthalpy between one state and another. Enthalpy change may be calculated under conditions of constant pressure.

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Enthalpy

Definition in Chemistry and Physics

by Anne Marie Helmenstine, Ph.D. 

Enthalpy is a thermodynamic property of a system.

It is the sum of the internal energy added to the product of the pressure and volume of the system.

It reflects the capacity to do non-mechanical work and the capacity to release heat.

Enthalpy is denoted as H; specific enthalpy denoted as h. Common units used to express enthalpy are the joule, calorie, or BTU (British Thermal Unit.)

Enthalpy in a throttling process is constant.

Change in enthalpy is calculated rather than enthalpy, in part because total enthalpy of a system cannot be measured.

However, it is possible to measure the difference in enthalpy between one state and another. Enthalpy change may be calculated under conditions of constant pressure.

Enthalpy Formulas

H = E + PV

where H is enthalpy, E is internal energy of the system, P is pressure, and V is volume

d H = T d S + P d V

What Is the Importance of Enthalpy?

·          Measuring the change in enthalpy allows us to determine whether a reaction was endothermic (absorbed heat, positive change in enthalpy) or exothermic (released heat, negative change in enthalpy.)

·         It is used to calculate the heat of reaction of a chemical process.

·          Change in enthalpy is used to measure heat flow in calorimetry.

·          It is measured to evaluate a throttling process or Joule-Thomson expansion.

·          Enthalpy is used to calculate minimum power for a compressor.

·         Enthalpy change occurs during a change in the state of matter.

·          There are many other applications of enthalpy in thermal engineering.

Example Change in Enthalpy Calculation

You can use the heat of fusion of ice and heat of vaporization of water to calculate the enthalpy change when ice melts into a liquid and the liquid turns to a vapor.

The heat of fusion of ice is 333 J/g (meaning 333 J is absorbed when 1 gram of ice melts.) The heat of vaporization of liquid water at 100°C is 2257 J/g.

Part A: Calculate the change in enthalpy, ΔH, for these two processes.

H₂O(s) → H₂O(l); ΔH = ?
H₂O(l) → H₂O(g); ΔH = ?

Part B: Using the values you calculated, find the number of grams of ice you can melt using 0.800 kJ of heat.

Solution

A. The heats of fusion and vaporization are in joules, so the first thing to do is convert to kilojoules. Using the periodic table, we know that 1 mole of water (H₂O) is 18.02 g. Therefore:
fusion ΔH = 18.02 g x 333 J / 1 g
fusion ΔH = 6.00 x 10³ J
fusion ΔH = 6.00 kJ
vaporization ΔH = 18.02 g x 2257 J / 1 g
vaporization ΔH = 4.07 x 10⁴ J
vaporization ΔH = 40.7 kJ

So the completed thermochemical reactions are:

H₂O(s) → H₂O(l); ΔH = +6.00 kJ
H₂O(l) → H₂O(g); ΔH = +40.7 kJ

B. Now we know that:

1 mol H₂O(s) = 18.02 g H₂O(s) ~ 6.00 kJ
Using this conversion factor:
0.800 kJ x 18.02 g ice / 6.00 kJ = 2.40 g ice melted

Answer

A. H₂O(s) → H₂O(l); ΔH = +6.00 kJ

H₂O(l) → H₂O(g); ΔH = +40.7 kJ

B. 2.40 g ice melted

Anne Marie Helmenstine, Ph.D.

Introduction

Ph.D. in biomedical sciences from the University of Tennessee at Knoxville - Oak Ridge National Laboratory.

Science educator with experience teaching chemistry, biology, astronomy, and physics at the high school, college, and graduate levels.

ThoughtCo and About Education chemistry expert since 2001.

Widely-published graphic artist, responsible for printable periodic tables and other illustrations used in science.

Experience

Anne Helmenstine, Ph.D. has covered chemistry for ThoughtCo and About Education since 2001, and other sciences since 2013. She taught chemistry, biology, astronomy, and physics at the high school, college, and graduate levels. She has worked as a research scientist and also abstracting and indexing diverse scientific literature for the Department of Energy.

In addition to her work as a science writer, Dr. Helmenstine currently serves as a scientific consultant, specializing in problems requiring an interdisciplinary approach. Previously, she worked as a research scientist and college professor. 

Education

Dr. Helmenstine holds a Ph.D. in biomedical sciences from the University of Tennessee at Knoxville and a B.A. in physics and mathematics with a minor in chemistry from Hastings College. In her doctoral work, Dr. Helmenstine developed ultra-sensitive chemical detection and medical diagnostic tests.

ThoughtCo and Dotdash

ThoughtCo is a premier reference site focusing on expert-created education content. We are one of the top-10 information sites in the world as rated by comScore, a leading Internet measurement company. Every month, more than 13 million readers seek answers to their questions on ThoughtCo.

For more than 20 years, Dotdash brands have been helping people find answers, solve problems, and get inspired. We are one of the top-20 largest content publishers on the Internet according to comScore, and reach more than 30% of the U.S. population monthly. Our brands collectively have won more than 20 industry awards in the last year alone, and recently Dotdash was named Publisher of the Year by Digiday, a leading industry publication.

https://www.thoughtco.com/definition-of-enthalpy-605091