Chapter 8.3-4 - Enthalpy and Thermochemical Equations
Reading Sheet
1.
The heat flow for a reaction system is denoted by the symbol
a. ∆Hreaction
b. ∆Treaction
c. qreaction
d. Hreaction
2.
There are many types of energy. Enthalpy is a type of _____.
a. thermal energy
b. chemical energy
c. calorie energy
d. light energy
3.
The symbol ∆H denotes _____.
a. change in energy
c. change in enthalpy
4.
Notes from Class Discussion:
Enthalpy
b. change in heat
d. change in temperature
Enthalpy change
Study Figure 8.4. For an exothermic reaction, the enthalpy of products is _____ than the enthalpy
of reactants. And for an endothermic reaction, the enthalpy of products is _____ than the enthalpy
of reactants.
a. less, less
b. greater, greater
c. less, greater
d. greater, less
5.
Which of the following statement(s) is(are) true of exothermic reactions? Select all that apply.
a. q > 0
b. ∆Hsystem < 0
c. Hproducts < Hreactants
d. Heat is absorbed by the system from the surroundings.
e. There is a negative enthalpy change.
6.
True or False: Scientists can use straightforward experiments to determine the absolute enthalpy
of a substance like water. _____________
If false, please explain your rationale or correct the statement.
7.
Study Figure 8.5. What is the observable evidence that the reaction is endothermic?
a. The temperature of the reaction decreases.
b. The temperature of the surroundings decreases.
c. There is a violent explosion.
d. Nonsense! The reaction is clearly exothermic.
8.
What is the sign of ∆H for the dissolving of NH4NO3 in water?
9.
Look up the word evolved in a dictionary. View the variety of uses. (See online dictionary.)
Explain in your own words what is meant when it is said that "185 kJ of heat is evolved."
10.
Study the thermochemical equation for the reaction of H2 with Cl2 to form HCl.
The reaction is ______.
a. endothermic
b. exothermic
In this reaction, 185 kJ of heat is evolved for every ______ of H2 which react.
a. 0.5 moles
b. 1.0 mole
c. 2.0 moles
d. 4.0 moles
a. Positive
Exothermic reactions
Endothermic reactions
b. Negative
Thermal stoichiometry
Heat can be thought of as a reactant or
a product term.
Determine the amount of heat evolved when 4.0 mol of HCl are formed: ___________ kJ
Determine the amount of heat evolved when 21.6 mol of HCl are formed: ___________ kJ
11.
Study Example 8.4 in order to answer the next two questions.
a.
Determine the ∆H when 7.0 mol of CH4 react with excess oxygen.
Heat of fusion
b.
Determine the ∆H when 3.00 L of CH4 are combined in a reaction vessel with 5.00 L of O2 at a
temperature of 25°C and a pressure of 1.00 atm.
Heat of vaporization
12.
The heat absorbed when a substance changes from solid phase to liquid phase is the heat of _____.
a. melting
b. vaporization
c. boiling
d. fusion
13.
Consider the thermochemical equation:
The 29.6 kJ refers to the heat of _____.
a. melting
b. vaporization
Br2(l)  Br2(g)
c. boiling
H2O(g)  H2 O(l)?
c 40.7 kJ
14.
Study Table 18.2. What is ∆H for:
a. 6.0 kJ
b. -6.0 kJ
15.
Consider the synthesis of sulfur trioxide from it's elements:
2 S + 3 O2  2 SO3
∆H = 790 kJ
What is the ∆H value for the decomposition of sulfur trioxide?
2 SO3  2 S + 3 O2 ∆H = _______ kJ
16.
17.
Then C  A + B
d. fusion
d. -40.7 kJ
e. 46.7 kJ
A
∆H4
B
If enthalpy were not a ______, then Hess's law would not be true.
a. state property
b. form of energy
c. stoichiometric quantity
Use Table 8.2 and Hess's Law to determine the ∆H for the following
process:
C6H6 (s)  C6H6 (g)
18.
If A + B  C ∆H = 520 kJ
∆H=29.6 kJ
∆H = _______kJ
Hess's Law
Three rules of thermochemistry
(p. 208)
1.
∆H3
C
∆H5
2.
∆H2
D
Consider the diagram at the right. Given that ∆H1 = 45 kJ, ∆H2 = 70 kJ,
∆H3 = 50 kJ, and ∆H5 = 205 kJ, determine the value of ∆H4?
∆H1
E
∆H = ______ kJ
3.