6.3 Heat Transfer and Thermal Equilibrium

Temperature reflects the average kinetic energy, or random motion, of particles. Kinetic energy is speed, so as temperature increases, molecules collide with the walls of the container faster.

Collision theory is based on the following postulates: 

To understand how collision theory works, it's useful to think of an analogy to break down the molecular processes. Let's say you're making lemonade. To make lemonade, you need to mix lemon juice, sugar, and water together. But just having the ingredients in the same place isn't enough to make lemonade - they need to interact with each other in just the right way.

Collision theory is like the "rules" for how ingredients can mix together to make a reaction happen. It says that for two things to react and form a new substance, they need to bump into each other with enough energy, in the right orientation, and often enough. Think of it like two billiard balls - if they don't hit each other hard enough, or at just the right angle, they won't react.

And just like how making lemonade faster would require you to mix the ingredients more quickly, the theory also explains how increasing the temperature or concentration of reactants can make the reaction happen faster by increasing the number and energy of collisions.

Successful collisions would therefore collide with proper orientation to break bonds and have enough energy to overcome the reaction’s activation energy.

If we look at this in terms of heat transfer, higher temperatures mean a higher number of collisions because the reactants are moving quickly. Heat conduction involves this high temperature state going to a low temperature state, where collisions are not as frequent due to the decrease in temperature.

As we see in real life, heat travels from a hot object to a cold object until the two are in thermodynamic equilibrium (thermal equilibrium). Take for example, putting a pan🍳 up against hot grates on a stove that are heated up by a fire. The heat travels from the grates to the pan until the two are the same temperature.

The Zeroth Law of Thermodynamics is stated as "if a is in thermal equil. with b and b is in thermal equil. with c, then a is in thermal equilibrium with c" where a, b, and c are bodies.