Chemistry – Unit 6
Name:______________________________________
Date:______________________ Per. #:_______
Unit 6 Exam Study Guide
Topics
Lesson 6.1 – Specific Heat
o Know the difference between heat and temperature. Know the correct units of each.
o Know what is meant by specific heat (C). Know that its units are J/g°C.
o Know how the specific heat of water compares to that of most metals.
o Know how to solve problems of changing temperature using the heat equation, Q = mCΔT.
Lesson 6.2 – Calorimetry and the Modified Heat Equation
o Know how to solve problems of two substances (i.e. water and a metal) reaching thermal equilibrium
using the modified heat equation: mCΔT = –mCΔT
Lesson 6.3 –Enthalpy
o Know what change in enthalpy (ΔH) is and how to use it to calculate the heat gained or lost in a
chemical reaction using stoichiometry.
o Know the difference between an exothermic and endothermic reaction and how to recognize each in
an energy diagram.
o Know the definitions of heat of formation and heat of combustion, how to right reactions for both, and
solve stoichiometry problems involving both.
Lesson 6.4 – Calorimetry II: Q and ΔH
o Understand the function and main components of a bomb calorimeter.
o Know how to solve calorimetry problems in which an enthalpy change of a reaction imparts heat to
and raises the temperature of water in a calorimeter.
Lesson 6.5 – Hess’s Law
o Know how to solve Hess’s Law problems by modifying formation reactions of the constituent
compounds and my modifying the subsequent enthalpies of formation, ΔHf.
Lesson 6.6 – Phase Changes
o Know how to read a phase change diagram for water.
o Know how to calculate the heat involved in vaporization/condensation, melting/freezing, and in
heating up solid, liquid, and gas forms of water.
Practice Problems
1. Using Enthalpy (ΔH)
Example
Using the reaction below, determine the
mass of carbon that must react to produce
700 kJ of heat.
C(s) + O2(g)  CO2(g) + 393.51 kJ
Practice
Using the reaction below, determine the amount of heat
released by the complete reaction of 50 grams of methane
(CH4).
CH4(g) + 2 O2(g)  CO2(g) + 2 H2O(l) + 890.31 kJ
Name:______________________________________
Date:______________________ Per. #:_______
2. The Heat Equation, Q = mCΔT
Example
How much heat is lost by 50 grams of iron if
it cools from 250°C to 25°C? The specific
heat of iron is 0.449 J/gK.
Practice
How much heat must be absorbed by a 15 g piece of calcium
metal to raise the temperature from 0°C to 100°C? Use the
back of the Heat of Formation handout to find the specific heat
of calcium.
3. The Modified Heat Equation, mCΔT = –mcΔT
Example
If silver has a specific heat of 0.057 Cal/g°C,
what will be the final temperature if 20 g of
silver at 300°C is placed in 120 g of water at
15°C?
Practice
What will be the final temperature if 45 g of iron at 250°C is
placed in 200 g of water at 25°C?
4. Hess’s Law
Example
Use Hess’s Law to calculate the heat of
reaction for the reaction of ammonia, NH3,
and hydrogen chloride, HCl, to produce
ammonium chloride, NH4Cl.
Practice
Use Hess’s Law to calculate the heat of reaction for the
reaction of ammonia, NH3, and oxygen gas to produce
nitrogen gas and water vapor.
4 NH3(g) + 3 O2(g)  2 N2(g) + 6 H2O(l)
NH3(g) + HCl(g)  NH4Cl(s)
Name:______________________________________
Date:______________________ Per. #:_______
5. Phase Change Diagram
Label the diagram below with all of the following terms:
 0°C
 100°C
 liquid water
 solid ice
 water vapor
 ΔHvap = 41 kJ/mol
 ΔHfus = 6 kJ/mol
 C = 4.18 J/g°C
 C = 2.06 J/g°C
 C = 1.87 J/g°C
6. Heat of Phase Changes
Example
How many kilojoules of energy would it take
for 25 grams of ice at 260 K to heat up, melt,
heat up, boil, and heat up of steam at 400 K?
Practice
How many kilojoules of energy are released when 100 grams
of water vapor at 120°C condenses into liquid water at 30°C?
Name:______________________________________
Date:______________________ Per. #:_______
7. Energy Diagram
a) Label the diagram below with all of the following terms:
 ΔHrxn
 Products
 Reactants
 Forward Reaction
 Reverse Reaction
b) How many kilojoules is ΔHforward?
d) How many kilojoules is ΔHreverse?
e) Is the forward reaction exothermic or
endothermic?
8. Q and ΔH
a) A 4-g sample of acetylene (C2H2) is combusted in a bomb calorimeter. The 1500 g of water in the
calorimeter raises from 23.5°C to 55.4°C. What is ΔHc for acetylene?
b) 4. How many grams of hexane would need to be combusted in a bomb calorimeter to raise the
temperature of 1000 g of water from 17.0°C to 49.9°C? Use ΔHc of hexane from your handout.