AnswersChemistry Credit Recovery BEnthalpy of Reaction

Enthalpy of Reaction — Unit test Answers

4 verified answers
1
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A metal sample is heated and placed into the water in a calorimeter at room temperature. Which statement best describes how the calorimeter can be used to determine the specific heat capacity of the metal sample?

A
Energy transfers to the metal from the water and calorimeter until they are all at room temperature.
B
Energy transfers from the metal to the water and calorimeter until they are all at room temperature.
C
Energy transfers to the metal from the water and calorimeter until they all reach a single temperature.
D
Energy transfers from the metal to the water and calorimeter until they all reach a single temperature.
2
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Which statement about enthalpy is true?

A
The enthalpy of formation for a pure element in its standard state is always positive.
B
The enthalpy of formation for a pure element in its standard state is always negative.
C
Enthalpy is a state function because its change depends only on initial and final conditions.
D
Enthalpy is not a state function because its change depends on the identities of the reactants and products.
3

A welding torch produces a flame by burning acetylene fuel in the presence of oxygen. This flame is used to melt a metal. Which energy transformation represents this process?

A
chemical energy into thermal energy
B
kinetic energy into potential energy
C
kinetic energy into electromagnetic energy
D
potential energy into chemical energy
4

Which best describes heat?

A
energy that is carried by electric and magnetic fields
B
energy that decreases as a car slows to a stop
C
energy that increases as a book is lifted to a higher shelf
D
energy that flows from a hot mug of tea to a cold hand
5

Which reaction is endothermic?

A
HCl + NaOH NaCl + H2O + 58 kJ
Option A
B
6CO2 + 12H2O + energy C6H12O6 + 6O2 + 6H2O
Option B
C
2Na + Cl2 2NaCl + energy
Option C
D
2C2H6 + 7O2 4CO2 + 6H2O + 2,502 kJ
Option D
6

Which energy changes in the enthalpy of solution are endothermic, and which are exothermic?

A
Hsolute and Hsolvent are endothermic; Hmix is exothermic.
Option A
B
Hsolute is endothermic; Hsolvent and Hmix are exothermic.
Option B
C
Hsolute is exothermic; Hsolvent and Hmix are endothermic.
Option C
D
Hsolute, Hsolvent, and Hmix are all exothermic.
Option D
7

Which is the most important factor in determining the state of a substance?

A
the size of the atoms in a substance
B
the number of molecules in a substance
C
the position of the electrons on the outer valence shells
D
the balance between intermolecular forces and kinetic energy
8

Consider the following intermediate chemical equations.When you form the final chemical equation, what should you do with CO?

Question illustration
A
Cancel out CO because it appears as a reactant in one intermediate reaction and a product in the other intermediate reaction.
B
Add the two CO molecules together, and write them as reactants in the final chemical reaction.
C
Write CO only once as a reactant in the final chemical reaction.
D
Write CO as a reactant and a product in the final chemical reaction.
9

Ammonia, NH3 (Hf = –45.9 kJ), reacts with oxygen to produce water (Hf = –241.8 kJ) and nitric oxide, NO (Hf = 91.3 kJ), in the following reaction:What is the enthalpy change for this reaction? Use .

Question illustration
A
–902 kJ
B
–104.6 kJ
C
104.6 kJ
D
900.8 kJ
10

Consider LiBr Li+ + and the following information.Hlat = –803 kJ/molHhydr of = –284 kJ/molHsol = –47 kJ/molWhat is the Hhydr of ? Use Hsol = –Hlat + Hhydr.

Question illustration
A
–570 kJ/mol
B
–566 kJ/mol
C
470 kJ/mol
D
472 kJ/mol
11

Which statement defines calorimetry?

A
the conservation of energy
B
a unit of energy that is used when calculating energy exchange
C
a device that is used to measure the heat that is gained or lost during a chemical change
D
the measurement of energy that is given off or absorbed in a physical or chemical process
12

H2O has a Hvap = 40.7 kJ/mol. What is the quantity of heat that is released when 27.9 g of H2O condenses?Use .

Question illustration
A
60.00 kJ
B
61.05 kJ
C
63.09 kJ
D
68.60 kJ
13

Consider the following intermediate chemical equations. The overall chemical equation is . To calculate the final enthalpy of the overall chemical equation, which step must occur?

Question illustration
A
Reverse the first equation, and change the sign of the enthalpy. Then, add.
B
Reverse the second equation, and change the sign of the enthalpy. Then, add.
C
Multiply the first equation by three, and triple the enthalpy. Then, add.
D
Divide the third equation by two, and double the enthalpy. Then, add.
14

Which statement best describes the direction of heat flow by conduction between two samples of the same material?

A
Heat flows from faster molecules to slower molecules when they are near.
B
Heat flows from faster molecules to slower molecules when they collide.
C
Heat flows from slower molecules to faster molecules when they are near.
D
Heat flows from slower molecules to faster molecules when they collide.
15

What explains the key difference between a bomb calorimeter and a coffee cup calorimeter?

A
A bomb calorimeter is 10 times larger but works the same way.
B
A bomb calorimeter measures heat for liquid products only.
C
A bomb calorimeter has a separate chamber to hold substances and can even measure heat gain or loss for reactions that do not occur in water.
D
A bomb calorimeter can measure heat gain or loss in gaseous reactions but is not useful for reactions that occur at high pressures and temperatures.
16

Two metal blocks that have slightly different temperatures are placed next to one another. After five minutes, they both have lower but equal temperatures. According to the law of conservation of energy, what most likely happened?

A
Energy was created inside the blocks.
B
Energy was destroyed inside the blocks.
C
Energy was absorbed into the blocks from outside the system.
D
Energy was transferred from the warmer block to the cooler block.
17

Find the enthalpy of hydration for an iodide ion in the process RbI . Use Hsol = –Hlat + Hhydr.Hsol = 31.0 kJ/molHlat = –630.0 kJ/molHhydr of Rb+ = –315.0 kJ/mol

Question illustration
A
–661.0 kJ/mol
B
–661 kJ/mol
C
–284.0 kJ/mol
D
–284 kJ/mol
18

Which direction does thermal energy flow in the following diagram?

Question illustration
A
Heat flows from the ice cream to the hand.
B
Heat flows from the hand to the ice cream.
C
The system is in a state of equilibrium.
D
The system is too cold for heat to move.
19

Complete combustion of a 0.350 g sample of a compound in a bomb calorimeter releases 14.0 kJ of heat. The bomb calorimeter has a mass of 1.20 kg and a specific heat of 3.55 J/(gi°C). If the initial temperature of the calorimeter is 22.5°C, what is its final temperature?Use .

Question illustration
A
19.2°C
B
25.8°C
C
34.2°C
D
72.3°C
20

Nitrogen dioxide, NO2(g) (Hf = 33.84 kJ/mol), is decomposed according to the following reaction:What is the enthalpy change when 2.50 mol of nitrogen dioxide decomposes? Use .

Question illustration
A
13.5 kJ of energy released
B
13.5 kJ of energy absorbed
C
84.6 kJ of energy released
D
84.6 kJ of energy absorbed

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