General Chemistry - Unit 13: Thermochemistry

Thermochemistry

The study of heat changes that occur during chemical reactions and physical changes of state.

Energy

The ability to do work or supply heat.

Heat

a form of energy

in what direction does heat flow

from warmer objects to cooler objects

When you add heat energy…

molecules move faster and temperature increases

Temperature

a measure of the average energy of molecular motion.

Chemical Potential Energy

stored energy in chemical bonds

Law of Conservation of (mass) Energy

Energy can neither be created nor destroyed, only converted from one form to another

1 Cal =

1000 cal

1 cal =

4.184 J

Calorimetry

Is the accurate and precise measurement of heat change for chemical and physical processes

calorimeter

device used to measure the amount of heat absorbed or released during these processes.

Temperature change is dependant on…

1. Amount of heat added

2. Mass of the substances

3. Composition of the substance (specific heat)

Specific heat

amount of heat required to raise the temperature of 1 gram of a substance by 1˚C

Specific heat of H2O

4.184 J/g˚C or 1.00 cal/g˚C

Thermochemical equation

A chemical equation which includes the energy used or produced in a chemical reaction.

Enthalpy

the internal energy or heat content of a substance at constant pressure.

exothermic reactions are shown two ways

1. energy is a product

2. H is negative

Endothermic reactions are shown two ways

1. H is positive

2. Energy is a reactant

heating curve

describes the enthalpy changes that take place during phase changes.

Molar heat of fusion

the amount of energy required to melt a substance

Molar heat of vaporization

the amount of energy required to vaporize (boil) a substance

Hess’s Law

If you add two or more chemical equations to get an overall equation, then you can also add the heat changes (ΔHs) to get the overall heat change