1. Ch. 17
THERMOCHEMISTRY

2. Thermochemistry
Thermochemistry: study of energy changes that occur during a chemical rxn and changes in state.
Enthalpy: heat content of a system (constant pressure)
Heat always flows from warmer to cooler objects.

3. System v. Surrounding System: part of universe you are studying
Could be a test tube, entire lab, or planet.
Surrounding: everything else.

4. Bond energy
Breaking bonds requires(absorbs) Energy while Forming bonds releases energy
Energy stored in chemical bonds is chemical potential energy.

5. H Delta H = enthalpy or heat of reaction ΔH = H products – H reactants
If products have more stored energy, answer is positive (energy was put into system)
If reactants have more stored energy, answer is negative (energy was released from system)
Energy of Products – energy of reactants
Units are calories (cal) or Kilojoules (kJ)
CH O2  CO H2O
Q = mCp T

6. Exothermic Rxns Exothermic System releases energy
Release means loses energy to surroundings
Means it gets warmer to us (we are surroundings)
Number that represents enthalpy is negative

7. Exothermic systems Ways to indicate an exothermic system
H = - # in kJ or cal (negative number)
CaO + H2O  Ca(OH) kJ

8. Exothermic Rxn

9. Endothermic Reactions
Endothermic System absorbs energy
Means it absorbs energy from surroundings
Means it gets cooler to us (we are surroundings)
Or energy must be provided(heat source [hotplate])
Number that represents enthalpy is positive

10. Endothermic Systems Ways to indicate an endothermic system
H = + # in kJ or cal (positive number)
2NaHCO kJ  Na2CO3 + H2O + CO2

11. Endothermic Rxn