# CHM 2045C: Spring Term 2008 Practice Final (Spring 1998's Test) Module Seven (Chapter 6)

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## Question 1

Which one of the following is not an endothermic process?

a) ice melting
b) water evaporating
c) boiling soup
d) condensation of water vapor

## Question 2

A chemical reaction that absorbs heat from the surroundings is said to be _________________ and has a
____________________ value of Δ H.

a) endothermic, positive
b) endothermic, negative
c) exothermic, negative
d) exothermic, positive
e) none of the above

## Question 3

The heat capacity of lead is 0.13 J/g·oC. How many joules of heat would be required to raise the temperature of 15 g of lead from 22oC to 37oC?

a) 2.0 J
b) -0.13 J
c) 5.8 X10-4 J
d) 29 J
e) none of the above

## Question 4

What is the resulting temperature when 35 g of water at 75oC is mixed with 15 g of water at 15oC?
(Heat capacity of water =4.184 J/g·oC)

a) 33oC
b) 48oC
c) 57oC
d) 120oC
e) none of the above

## Question 5

Using the thermochemical equations below, which one of the following choices is correct for the calculation of the change in heat of the following reaction?
Mg3N2 + 3H2O --> 3MgO + 2NH3 Δ Hrxn=?

3Mg + N2   -->   Mg3N2         Δ H1
H2 + (1/2)O2 --> H2O           Δ H2
Mg + (1/2)O2 --> MgO         Δ H3
(1/2)N2 + (3/2)H2 --> NH3       Δ H4

a)   ΔHrxn = ΔH1 + ΔH2 + ΔH3 + ΔH4

b)   ΔHrxn = ΔH1 + ΔH2 - ΔH3 - ΔH4

c)   ΔHrxn = 2ΔH4 + 4ΔH3 - ΔH2 - 3ΔH1

d)   ΔHrxn = ΔH1 - ΔH2 - ΔH3 - ΔH4

e)   ΔHrxn = 3ΔH3 + 2ΔH4 - ΔH1 - 3ΔH2

## Question 6

The following reactions occur for the hypothetical element E:
2E(l) + O2(g) --> 2EO(g)     Δ Ho = -333kJ
EO(g) + O2(g) --> EO3(s)     Δ Ho = -196kJ
What is the ΔH in kJ for the reaction:
2E(l) + 3O2(g) --> 2EO3(s)?

a) -526 kJ
b) +526 kJ
c) +725 kJ
d) -725 kJ
e) -137 kJ

## Question 7

Use the ΔH values for equations 1 & 2 to determine the value of ΔH for equation 3.
(1) 2NO --> N2 + O2         Δ H = -180kJ
(2) 2NO + O2 --> 2NO2    Δ H = -112kJ
(3) N2 + 2O2 --> 2NO2     Δ H = ?

a) 68 kJ
b) -68 kJ
c) -292 kJ
d) 292 kJ

## Question 8

The energy released by combustion of 1 g of a substance is called that substance's

a) specific heat
b) fuel value
c) nutritional calorie
d) heat capacity

## Question 9

A 2.15-g sample of benzene (C6H6) is burned in a bomb calorimeter, and the temperature rises from 22.46 oC to 34.34oC. Calculate the heat capacity of the bomb calorimeter. Note the following thermochemical equation:
C6H6 (l) + 15/2 O2 (g) ------> 6CO2(g) + 3H2O (g)      Δ Ho = -326705 kJ

a) 1.52 x 103 kJ oC-1
b) 7.58 kJ oC-1
c) 90.1 kJ oC-1
d) 35.3 kJ oC-1
e) 128 kJ oC-1

## Question 10

Given the thermochemical equation,
H2 (g) + Cl2 (g) -----> 2HCl (g)      Δ Ho= -18406 kJ
calculate Δ Ho for the reaction

HCl (g) -----> 1/2 H2 (g) + 1/2 Cl2 (g)

a) +18406 kJ
b) -9203 kJ
c) +9203 kJ
d) +369.2 kJ
e) -369.2 kJ

## Question 11

A 28.5-g sample of iron is heated to 95.0o C and then dropped into 58.0 g of water in a coffee-cup calorimeter. The temperature of the water rises from 23.5o C to 27.1o C. Calculate the specific heat of iron.

a) 0.11 J g-1oC-1
b) 0.45 J g-1oC-1
c) 2.2 J g-1oC-1
d)1.6 x 102 J g-1oC-1
e) 7.8 x 10-3 J g-1oC-1

## Question 12

Calculate Δ Ho for the following reaction using the given enthalpies of formation.

2NO (g) + 5O2 (g) ----> 2NO2 (g)
Δ Hof NO (g) = 90.25 kJ/mol
Δ Hof NO2 (g) = 33.18 kJ/mol

a) +57.07 kJ
b) -57.07 kJ
c) +114.14 kJ
d) -114.14 kJ
e) +66.36 kJ

## Question 13

Use the following thermochemical equations

C2H5OH (l) + 3 O2 (g) ----> 2CO2 (g) + 3H2O (l)      Δ Ho = -1367 kJ

H2 (g) + 1/2 O2 (g) -----> H2O (l)       Δ Ho = -286 kJ

C (gr) + O2 (g) -----> CO2 (g)       Δ Ho = -394 kJ
to calculate the enthalpy change for the reaction

2C (gr) + 3H2 (g) + 1/2 O2 (g) ------> C2H5OH (l)      Δ Ho = ?

a) +2047 kJ
b) -279 kJ
c) +687 kJ
d) +279 kJ
e) +680 kJ

## Question 14

When 10 g samples of the following materials absorb 100 J of heat, the temperature increase indicated is observed. Which material has the largest specific heat?

a) water 2 K
b) wood 6 K
c) copper 26 K
d) cement 11 K
e) glass 12 K

## Question 15

An endothermic reaction is carried out in a cofffe-cup calorimeter. Which statement is incorrect for this process?

a) The temperature of the water decreases.
b) The enthalpy change for the reaction equals qH2O.
c) Heat is absorbed from the water.
d) The enthalpy change for the reaction is positive.
e) The products have higher enthalpy than the reactants.

## Question 16

Which statement is not correct?

a) Internal energy, E, is a function of state.
b) Heat and work are state functions.
c) Heat is given off to the surroundings in an exothermic reaction.
d) The enthalpy change is the heat of reaction at constant pressure.
e) Enthalpy is a function of state.

## Question 17

How does the change in temperature relate to an object's mass and its specific heat, respectively, for a given input of heat?

a) directly, directly
b) directly, inversely
c) inversely, inversely
d) inversely, directly
e) depends on the object

## Question 18

Given the following equation,
2 H2 (g) + O2 (g) ------> 2 H2O (l)      Δ Ho = -571.6 kJ/mol.
which statement is incorrect?

a) Δ Ho for the reverse reaction is +571.6 kJ/mol.
b) Δ Ho for forming one mole of liquid water is -285.8 kJ/mol.
c) Δ Ho for the reaction of one-half mole of oxygen is -285.8 kJ/mol.
d) The equation forming gaseous water would have a different Δ Ho.
e) The standard heat of formation of liquid water is -571.6 kJ/mol.

## Question 19

Which is correct regarding an endothermic reaction?

a) The reaction does not occur.
b) The reaction liberates heat.
c) The enthalpy of the reactants is higher than the enthalpy of the products.
d) The sign of the Δ H is positive.
e) The temperature increases when the reaction is carried out in a calorimeter.

## Question 20

A 73.6 g sample of aluminum is heated to 95.0o C and dropped into 100.0 g of water at 20.0o C. If the resulting temperature of the water is 30.0o C, what is the specific heat of the metal?

a) 0.143 cal/g * o C
b) 0.209 cal/g * o C
c) 0.418 cal/g * o C
d) 0.486 cal/g * o C
e) 0.679 cal/g * o C

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