Chemistry of Cooking

Laws of Thermodynamics

The research for this unit begins with the origins of thermodynamics.  This is the foundation for comprehension of states of matter and heat.  Over the years, four laws of thermodynamics have been discovered.  However, since only three of the laws are relevant to this project; those will be the ones explained.  They are the zeroth, first, and second laws of thermodynamics.  The discovery of these laws are credited to decades of work by a vast group of pioneers including but not limited to: Carnot, Kelvin, Clausius, Gibbs, Helmholtz, Joule, Maxwell, and Mayer.¹ There is much debate regarding the founder of each law.  Comprehending each person’s contribution to thermodynamics would need extensive research and a broader understanding of thermodynamics than this unit warrants.   

The zeroth law states “If two thermodynamic systems are each in thermal equilibrium with a third, then they are in thermal equilibrium with each other”.² This means that you have three objects. The first object has no net heat transfer with the second.  The second objects has no net heat transfer with the third. Then, without measuring it you know that the first and third object also have no net heat transfer.   Basically, if you put a slice of pie on a plate and you stick a fork into the pie then walk away for a bit.  After a while, you know that all three of them will be in thermal equilibrium with each other.  This law was discovered after the first law but was deemed the vital foundation for thermodynamics; hence, it was named the zeroth law.  

Next, is the first law which states “energy cannot be created or destroyed; only changed”.³ This means that energy does not just appear when we need it but must come from elsewhere.  If you eat food then your body converts the chemical energy to kinetic energy.  The burst of energy did not just suddenly manifest; it changed forms. 

After that, is the second law of thermodynamics.  Heat will always be transferred from the hot object to the cold object.⁴ This means that if you place a hot item and a cold item together then the heat will always transfer to the cold item.  This applies to the object being left alone and not being forced to change temperature as they would in a freezer.  An example for this is a cup of hot tea.  The heat from the tea transfers to its environment.  It also works in reverse, a cup of iced tea will have the heat of its environment transferred to it.  The heat always transfers to the cold with the objects always wanting to achieve equilibrium. 

These laws built a solid understanding of thermodynamics in my mind. Yet I was still wondering what is heat and how it transfers to states of matter.  Upon researching heat, I found a clear explanation. “The amount of heat in a substance is the total vibrational energy of all the atoms and molecules that make up the substance”.⁵ An important tidbit to remember it that heat and temperature are two different things.  Heat is the vibrational energy of all of the molecules and temperature is the average heat per molecule.  That was easy to understand, so I ensued with researching how heat transfers to molecules.