Enthalpy

Enthalpy

Physics and Chemistry _{but mostly just chemistry.}

Think about when you combine a strong acid like hydrochloric acid and a strong base like lye.

They will EXPLODE.

For those of you who have seen a video of this experiment before, you know it actually just froths and shoots everywhere.

Enthalpy is the property of matter to spread out and make space for itself when it is heated up.

Thermodynamics is a branch of physics and chemistry that studies the relations between matter, energy and heat.

What’s the difference between entropy and enthalpy?

Multiple Choice

What is the zeroeth law of Thermodynamics?

• If two systems are in equilibrium with another system, they are all in equilibrium.

• When energy passes through a system, the energy in that system is affected.

• Heat cannot spontaneously pass from one body to another. Perpetual motion machines are impossible because too much energy will dissipate, and eventually, all energy will be lost.

• Entropy in a system will approach zero when the temperature of the system is at absolute zero

Please listen closer next time.

You all get Fs for the rest of the year.

That was actually a joke.

You may laugh.

A quick video demonstration:

All eyes up front!

Multiple Choice

Why does matter heat up as the system it is in shrinks in size?

• Because the molecules bump off of themselves more slowly, which generates more heat.

• Because the molecules bump off of themselves more rapidly and frequently, which generates less heat.

• Because the molecules bump off of themselves more rapidly and frequently, which generates more heat.

Multiple Choice

True or false: an open can of soda has less enthalpy than a closed can of soda.

• True

• False

The open can of soda has more enthalpy, because the gasses in it have spread out more.

This equation allows you to calculate enthalpy.

ΔH=ΔE+ΔPV

Change in enthalpy equals the change in the system's energy plus the change in pressure multiplied by the volume.

Enthalpy, or ΔH

ΔH=ΔE+ΔPV.

ΔE, or change in energy

ΔH=ΔE+ΔPV

ΔPV, or change in pressure times volume

ΔH=ΔE+ΔPV

ΔH=ΔE+ΔPV or H=E+PV

Remember that if you remove the delta symbol which represents change, the forumla will still be true.

The correct answer is 2,330,958 joules per mole. Tips:

• Make sure to use the unit joules or joules per mole. Use the following: j, joules/mole, joules per mole, joules.

• Being more precise is great, so do not round your number.

• Remember to add commas if the answer is in the thousands.

• Also, remember that if the number is diminishing, you need to subtract in the equation. (Foreshadowing!)

The change in enthalpy is 1,065,477.5 joules per mole less than it was before. Tips:

• Remember that change is not negative. Change will always be a positive value.

• Remember again to use units and add commas. You did not get the answer right if you did not add commas this time, because I have a limit of five correct answers.

Calorimetry: Calorimetry is a principle and a group of equations that allow you to calculate how much heat an object will give off when you raise the temperature.

Open Ended

Of course, it's all about heat. Why is heat so important in physics and chemistry but in everything as well?

Why is heat so important?

Back to the Calorimetry.

I am going to share an equation with you all. We're going to break it down, talk about each part and then wrap it all up with a problem for you to solve.

ΔH=smΔT

Change in heat is equal to the specific heat of the substance multiplied by the total mass of the substances and the change in temperature. In other words, the change in how much heat a substance is going to emit is easily determined by how much energy is needed to heat an object times how much of the substance there is times the temperature, which is not the same thing as heat.

First part: Change in heat or ΔH.

ΔH=smΔT

Next: Specific heat, or s

ΔH=smΔT

After that: Mass, or m

ΔH=smΔT

Last: Change in temperature or ΔT

ΔH=smΔT

ΔH=smΔT

The change in heat or ΔH is equal to 69630.3 Joules

That means that the water is releasing approximately 70,000 joules more than it was before.

ΔH is equal to 633.672 joules

This means that the water is releasing approximately 70,000 joules more than it was before.

Please take one good long look at the formula. ΔH=smΔT. No parts of the problem given are going to be highlighted.

And, recall the enthalpy formula, H=E+PV. This is the final test, and these last two questions will use both the enthalpy formula and the calorimetry formula.

Multiple Select

What are some practical applications of caliometry? Select ALL that apply.

• Hand warmers

• Treadmills

• Ice melt

• Maintaining the temperatures of computer parts

Multiple Choice

What is enthalpy?

• A concept of thermodynamics explaining the spread of matter based on the temperature

• A concept of thermodynamics explaining the spread of energy

• A concept of thermodynamics disproving the possibility of perpetual motion machines

• A concept of thermodynamics that defines absolute zero.

Multiple Choice

What is calorimetry?

• A group of equations that explain physics

• The specific heat of water

• A formula to calculate specific heat

• A group of formulas that calculate the generation of heat.

• A way of watching what you eat

Bibliography

• “Calorimetry and Enthalpy.” Performance by Hank, Crash Course, youtu.be/6y5oO6NfGHw. 

• Performance by Salman Khan, Enthalpy, Khan Academy, youtu.be/fucyI7Ouj2c. 

• Phet Simulations. “States of Matter - Basics.” Phet, University of Colorado - Boulder, phet.colorado.edu/sims/html/states-of-matter-basics/latest/states-of-matter-basics_en.html.