Topics:
Laws of Thermodynamics
Heat vs Temperature
Calculating Energy Changes (with temperature change)
Enthalpy
Representing enthalpy

Thermodynamics

The study of energy and energy movement is called thermodynamics. Two laws govern the movement of heat in nature between objects. These rules are termed the two laws of thermodynamics or heat movement.

Laws of Heat Movement

a) 1st law of Thermodynamics: Law of conservation of energy.

Energy is never lost or gained , it only changes form. Energy can have many forms, for example light, heat, and sound. This law states that energy can change form but is never really lost in any closed system.

When an exothermic reaction occurs some of the molecular enthalpy (energy in the molecules ) of the system is converted into heat or light. This energy is then released by the system to the surroundings. The total energy of the system decreases, but the energy of the surroundings increases by the same amount. We can therefore state

Energy _{( system)} = - Energy _{(surroundings)}

When an endothermic reaction occurs some of the energy in the surroundings is absorbed and converted to molecular enthalpy.

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b) 2nd law of Thermodynamics:

Heat Energy always travels spontaneously from a warmer body (body with higher temperature) to a colder body.

You have known since you were a child that if you touch a hot stove you get burned. This is the second law of thermodynamics in action. The stove is warmer than your body and therefore transfers heat to your hand. When you go outside without protection, when it is cold, you may get frostbite. This is another example of the second law of thermodynamics in action. The heat from your body is moving into the surrounding air, when your body can no longer replace the heat as fast as it is being lost, your skin freezes and you get frostbite.

Check your understanding 1) What exactly happens to the skin when you get frostbite? 2) Research first aid treatments and determine how frostbite is treated. 3) Show how the 1st and 2nd law of thermodynamics is applied to the first aid treatment for frostbite? 4) Repeat questions 1-3 but this time for burns of the skin.

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