AnswersChemistryEnergy in Chemical Reactions

Energy in Chemical Reactions — Test Answers

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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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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 electromagnetic energy
C
kinetic energy into potential energy
D
potential energy into chemical energy
3

How is the kinetic energy of the particles of a substance affected during a phase change?

A
Kinetic energy increases during exothermic changes and decreases during endothermic changes.
B
Kinetic energy changes in the opposite way that the potential energy changes.
C
Kinetic energy does not change, but the potential energy does.
D
Kinetic energy decreases during exothermic changes and increases during endothermic changes.
4

Which reaction is endothermic?

A
2 Na plus Cl sub 2 rightarrow 2 NaCl plus energy
B
HCl plus NaOH rightarrow NaCl plus cap h sub 2 cap o plus 58 kJ
C
6 CO sub 2 plus 12 cap h sub 2 cap o plus energy rightarrow cap c sub 6 cap h sub 12 cap o sub 6 plus 6 cap o sub 2 plus 6 cap h sub 2 cap o
D
2 cap c sub 2 cap h sub 6 plus 7 cap o sub 2 rightarrow 4 CO sub 2 plus 6 cap h sub 2 cap o plus 2 comma 502 KJ
5

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

A
Heat flows from slower molecules to faster molecules when they collide.
B
Heat flows from faster molecules to slower molecules when they are near.
C
Heat flows from faster molecules to slower molecules when they collide.
D
Heat flows from slower molecules to faster molecules when they are near.
6

Complete combustion of a 0 point 3 5 0 g sample of a compound in a bomb calorimeter releases 14 point 0 kJ of heat. The bomb calorimeter has a mass of 1 point 2 0 kilograms and a specific heat of 3 point 5 5 the fraction with numerator cap j and denominator open paren g times degree cap c close paren If the initial temperature of the calorimeter is 22 point 5 times degree C , what is its final temperature? Use q is equal to m cap c sub p triangle cap t

A
19 point 2 times degree C
B
34 point 2 times degree C
C
72 point 3 times degree C
D
25 point 8 times degree C
7

cap h sub 2 cap o has a triangle cap h sub vap is equal to 40 point 7 kJ over mol What is the quantity of heat that is released when 27 point 9 g of cap h sub 2 cap o condenses? Use q is equal to n triangle cap h

A
63 point 0 9 kJ
B
61 point 0 5 kJ
C
60 point 0 0 kJ
D
68 point 6 0 kJ
8

Which best describes heat?

A
energy that is carried by electric and magnetic fields
B
energy that increases as a book is lifted to a higher shelf
C
energy that decreases as a car slows to a stop
D
energy that flows from a hot mug of tea to a cold hand
9

Ammonia, NH sub 3 , Δ⁢H_f=−46.2kJ reacts with oxygen to produce water Δ⁢H_f=−241.8kJ and nitric oxide, NO , Δ⁢H_f=91.3kJ , in the reaction: 4 NH sub 3 g plus 5 cap o sub 2 g rightarrow 6 cap h sub 2 cap o g plus 4 NO g What is the enthalpy change for this reaction? Use Δ⁢H_rxn=∑(Δ⁢H_f_1p⁢r⁢o⁢d⁢u⁢c⁢t⁢s)−∑(Δ⁢H_f_1r⁢e⁢a⁢c⁢tan⁡t⁢s)

A
900 point 8 kJ
B
104 point 6 kJ
C
negative 104 point 6 kJ
D
negative 900 point 8 kJ
10

Which statement about enthalpy is true?

A
The enthalpy of formation for a pure element in its standard state is always positive.
B
Enthalpy is a state function because its change depends only on initial and final conditions.
C
Enthalpy is not a state function because its change depends on the identities of the reactants and products.
D
The enthalpy of formation for a pure element in its standard state is always negative.
11

Nitrogen dioxide, NO sub 2 times g Δ⁢H_f=33.84kJ/mol , is decomposed according to the reaction: 2 NO sub 2 g rightarrow cap n sub 2 times g plus 2 cap o sub 2 g What is the enthalpy change when 2 point 5 0 mol of nitrogen dioxide decomposes? Use Δ⁢H_rxn=∑(Δ⁢H_f_1p⁢r⁢o⁢d⁢u⁢c⁢t⁢s)−∑(Δ⁢H_f_1r⁢e⁢a⁢c⁢tan⁡t⁢s)

A
13 point 5 kJ of energy absorbed
B
13 point 5 kJ of energy released
C
84 point 6 kJ of energy released
D
84 point 6 kJ of energy absorbed
12

Consider these intermediate chemical equations. cap c times s plus cap o sub 2 times g rightarrow CO sub 2 times g triangle cap h sub 1 is equal to negative 393 point 5 kJ 2 CO g plus cap o sub 2 times g rightarrow 2 CO sub 2 g triangle cap h sub 2 is equal to negative 566 point 0 kJ 2 cap h sub 2 cap o g rightarrow 2 cap h sub 2 g plus cap o sub 2 times g triangle cap h sub 3 is equal to 483 point 6 kJ The overall chemical equation is C(s)+H_2​O(g)→CO(g)+H_2​(g) To calculate the final enthalpy of the overall chemical equation, which step must occur?

A
Multiply the first equation by three, and triple the enthalpy. Then, add.
B
Divide the third equation by two, and double the enthalpy. Then, add.
C
Reverse the second equation, and change the sign of the enthalpy. Then, add.
D
Reverse the first equation, and change the sign of the enthalpy. Then, add.
13

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

A
the position of the electrons on the outer valence shells
B
the balance between intermolecular forces and kinetic energy
C
the size of the atoms in a substance
D
the number of molecules in a substance
14

Consider these intermediate chemical equations. cap c times s plus 1 half cap o sub 2 g rightarrow CO times g CO times g plus 1 half cap o sub 2 g rightarrow CO sub 2 times g When you form the final chemical equation, what should you do with CO ?

A
Add the two CO molecules together, and write them as reactants in the final chemical reaction.
B
Write CO only once as a reactant in the final chemical reaction.
C
Cancel out CO because it appears as a reactant in one intermediate reaction and a product in the other intermediate reaction.
D
Write CO as a reactant and a product in the final chemical reaction.
15

Which describes the enthalpy change associated with an endothermic reaction?

A
It is negative because the enthalpy of the reactants is greater than the enthalpy of the products.
B
It is negative because the enthalpy of the products is greater than the enthalpy of the reactants.
C
It is positive because the enthalpy of the products is greater than the enthalpy of the reactants.
D
It is positive because the enthalpy of the reactants is greater than the enthalpy of the products.
17

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

A
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.
B
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.
C
A bomb calorimeter measures heat for liquid products only.
D
A bomb calorimeter is 10 times larger but works the same way.
18

Which is the best example of how electromagnetic energy is used in everyday life?

A
a car burning gasoline to power the engine
B
a car of a roller coaster moving quickly down a slope
C
a pot of boiling water on a gas stove
D
a patient receiving an X-ray in a hospital
19

How should the baking of a pizza be categorized?

A
as an exothermic process because the dough releases heat
B
as an endothermic process because the dough absorbs heat
C
as an endothermic process because the dough releases heat
D
as an exothermic process because the dough absorbs heat
20

Which statement defines calorimetry?

A
a device that is used to measure the heat that is gained or lost during a chemical change
B
the conservation of energy
C
the measurement of energy that is given off or absorbed in a physical or chemical process
D
a unit of energy that is used when calculating energy exchange
21

Consider these intermediate chemical equations. cap c times s plus 1 half cap o sub 2 g rightarrow CO times g CO times g plus 1 half cap o sub 2 g rightarrow CO sub 2 times g How will oxygen appear in the final chemical equation?

A
cap o sub 2 times g as a reactant
B
cap o times g as a product
C
2 cap o g as a reactant
D
cap o sub 2 times g as a product

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