Chemical Thermodynamics

Studying Hot Stuff

Thermodynamics is the branch of science studying the relationship between heat and various forms of energy. Chemical thermodynamics is the branch of thermodynamics that studies the relationship of heat exchange to chemical reactions.

One misconception that must be overcome is the difference between heat and temperature. The following video will give overview of both of those ideas.

When we think about the relationship between chemical reactions and energy, there are three possible options.

1. energy is lost
2. energy is gained
3. energy is neither gained nor lost

Option 3 really isn't an option, since essentially ALL chemical reactions involve the breaking and making of chemical bonds, and those process always involve an energy change.

When energy is lost (or EXits) from a chemical system, the reaction is said to be EXOTHERMIC. Similarly, when energy ENters a chemical system, the reaction is called an ENDOTHERMIC reaction.

The next video gives an excellent discussion about these types of reactions.




Not all energy changes result in temperature changes. Believe it or not, heat can enter or leave a situation and there will NOT be a change in temperature. This can happen during a phase change. What is happening in that case is that the energy is involved in making or breaking chemical bonds, but not in increasing or decreasing the kinetic energy of the molecules. Remember, temperature is the measurement of the average kinetic energy of the molecules of a substance. Thus, it appears that the POTENTIAL, not kinetic, energy of the system is changing.

The following video will go more into depth on the relationship between phase changes and energy changes.




Two measurable characteristics of the phase changes involved in common substances are the latent heat of fusion and the latent heat of vaporization. If you watch some of the crime solving TV programs, you have heard the term "latent fingerprints." The word latent means "hidden" in the sense that it is there, but not easily visible. We can, however, figure out ways to make something that is latent visible for observation.

Thus, latent heats of fusion (melting) or vaporization (liquid turning to vapor) can be measured and calculated. We will be doing a lab in which we will measure the latent heat of fusion of water.

Watch the following video to get a grasp on the energy changes involved in phase changes. Always keep remembering, phase changes do NOT involve temperature changes, but only potential energy changes.





Similar to the latent heat of fusion is the energy involved when a liquid changes into a gas at the boiling point of the liquid. This energy is called the latent heat of vaporization. As you watch the next video, look for similarities and differences between the heat of fusion and the heat of vaporization.




The next concept does involve a temperature change. Specific heat is a characteristic of various substances that can be a factor in identifying the substance. Specific heat is defined as the amount of heat necessary to raise the temperature of one gram of a substance one degree Celsius.

You will find that water has one of the highest specific heats (molten lithium is higher... but not very common). That high specific heat of water has a radical effect on the microclimates we live in and many of the other common characteristics of water.