Thermochemistry

Thermo-Chemistry

the study of energy changes that occur during chemical reactions and changes of state.

Chemical Potential Energy: the energy stored in the chemical bonds of a substance.

Heat: (q) energy that transfers from one object to another because of a temperature difference between them.

Exothermic and Endothermic

System: the part of the universe on which you focus your attention.

Surroundings: everything else in the universe besides the “system”.

Law of Conservation of Energy

in any chemical or physical process energy is neither created nor destroyed.

Endothermic Process

one that absorbs heat from the surroundings. The system gains heat as the surroundings cool down.

Exothermic Process

one that releases heat to its surroundings. The system loses heat as the surroundings heat up.

Heat Flow

measured in two common units, the calorie and joule.

calorie: the amount of heat required to raise 1 gram of water 1 ) C.

Calorie: food Calorie is equal to 1000 calories.

1 Calorie = 1 kilocalorie = 1000 calories

joule: the amount of heat required to raise 1 gram of water 0.239 ) C. The SI unit of energy.

1 J = 0.239 calories 4.184 J = 1 calorie

Heat Capacity and Specific Heat

Heat Capacity: amount of heat needed to increase the temperature of an object 1 ) C.

Specific Heat Capacity: amount of heat needed to increase 1 gram of an object 1 ) C.

High Specific Heat Capacity

Means an object gains or loses heat slowly due to the high capacity for heat.

Low Specific Heat Capacity

Means an object gains or loses heat rapidly due to the low capacity for heat.

Calorimetry The heat released by the system is

equal to the heat absorbed by its surroundings. Conversely, the heat absorbed by a system is equal to the heat released by its surroundings.

Enthalpy (H) The same as the heat content of a

system at constant pressure. The heat released or gained by a system is the same as the change in enthalpy (ΔH).

If pressure is constant Q= ΔH

Heat and Changes of State ΔH fusion: the heat absorbed as a

substance goes from a solid to a liquid.

ΔH solidification: the heat released or lost as a substance goes from a liquid to a solid

ΔH vaporization: the heat absorbed as a substance goes from a liquid to a vapor.

ΔH condensation: the heat released or lost as a substance goes from a vapor to a liquid.