Thermochemistry Review
What you need to know:
 Difference between endothermic and exothermic reactions
o Breaking/forming bonds
o +/- q
o +/- ΔH
o How it feels
o Energy on the products or reactants side of equation
o Where energy comes from (surrounding/system)
o Where the energy goes to (surrounding/system)
o Energy curve
o Products or reactants have more energy?
 Specific heat
o Symbol for specific heat
o Unit for specific heat
o Compare substances with different specific heats  which will heat/cool faster?
o Use specific heat in equation q=mcΔT
o Use q=mcΔT to find mass, temp, or energy
 Thermal equilibrium
o What does it mean?
o How do you know if two substances have reached thermal equilibrium?
o How does heat flow/travel between objects?
 Kinds of heat transfer:
o Conduction
o Convection
o Radiation
o Examples of each kind
 Phase changes
o Draw a phase change diagram of a substance from one temp. to another
o Use q=nΔH to solve for energy of a phase change
o Determine what is happening on each part of a phase change diagram for water
o Which parts are temp. changes?
o Which parts are phase changes?
o Which equation do you use for each part?
 Thermochemical Equations:
o Determine if the reaction is endo/exothermic
o Find the moles from energy
o Find energy from moles
o Find energy from mass
o Find mass from energy
 Hess’s Law
o Calculate ΔH of a chemical reaction using smaller, step reactions
o Flip equations AND/OR multiple equations
 Bond dissociation
o Calculate overall ΔH when given a chemical equation
o Determine bond energy from chart for molecules/bonds
 Heating/Cooling Curves:
o Use q=mcΔT and q=nΔH to find total energy of water heating/cooling
o Determine what is happening on each part of a phase change diagram for water
o Which parts are temp. changes?
o Which parts are phase changes?
o Be able to draw the correct heating/cooling curve
Potentially useful information
q=mcΔT
q=nΔH
Cwater= 4.184 J/g°C
Csteam=cice= 2.0 J/g°C
ΔHfus= 6.0 kJ/mol
ΔHvap= 40.7 kJ/mol
1. Determine the ΔH for this reaction:
Melting point H2O = 0 °C
Boiling point H2O = 100 °C
2 C(s) + 2 H2O(g)  CH4(g) + CO2(g)
C(s)  H2O (g)  CO (g)  H2 (g)
H  131.3 kJ
CO (g)  H2O (g)  CO2 (g)  H2 (g)
CH4 (g)  H2O (g)  3 H2 (g)  CO (g)
H  - 41
H  206.1
2. Label, what phase or what phase change corresponds with each of the numbers. Write what equation you would
use for each of the numbers. State the melting point and boiling point of the substance.
1:
2:
3:
4:
5:
3. For the following reaction: 4Fe + 3O2  2Fe2O3 + 70 kJ
a) How much heat is produced when 3 moles of Fe react?
b) How much heat is produced when 38 grams of oxygen react?
4. Write endothermic or exothermic for each of the following
- ΔH
A + B  C + heat
A hot pack
+q
bonds breaking
more energy in products than reactants
heat is released
Bonds forming
heat transferred from surroundings to the system
Cold to the touch
5. What is the heat needed to raise 70 grams of metal (specific heat 0.44 J/gC) from 20 deg C to 80 deg C?
How much heat is RELEASED when 100 grams of water (specific heat 4.184 J/gC) cool from 75 deg C to 62 deg C?
What is the amount of energy needed to melt 50 grams of water at its melting point?
6. Find the ΔH of the reaction using the bond dissociation chart:
C2H6
+
Br2
Br - Br

CH5Br
+
HBr
Br
+ H - Br
7. Draw the heating/cooling curve when 40 grams of ice at -5°C is heated to steam at 125°C and calculate the heat (q)
needed to make that process happen.