AnswersChemistryEnergy in Chemical Reactions

Energy in Chemical Reactions — Test Answers

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1
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What does this piece of evidence best support?

A
the effect of pressure on reaction rates
B
the Maxwell-Boltzmann distribution
C
the effect of temperature on reaction rates
D
the collision theory
2
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From first to last, which lists the order in which these samples will reach 90 point 0 times degree C ?

A
Al , Fe , Zn , Ag
B
Ag , Al , Zn , Fe
C
Ag , Zn , Fe , Al
D
Al , Fe , Ag , Zn
3

Molecules that have longer arrows are moving faster. Which statement describes what is happening in this system?

A
There is no change in average kinetic energy between these two systems.
B
Kinetic energy decreases as temperature decreases.
C
Temperature is not related to the average kinetic energy of a system.
D
Molecules vibrate more as temperature decreases.
4

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 absorbed into the blocks from outside the system.
B
Energy was created inside the blocks.
C
Energy was destroyed inside the blocks.
D
Energy was transferred from the warmer block to the cooler block.
5

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
negative 900 point 8 kJ
C
104 point 6 kJ
D
negative 104 point 6 kJ
6

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 can measure heat gain or loss in gaseous reactions but is not useful for reactions that occur at high pressures and temperatures.
D
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.
7

Which statement best applies collision theory to preventing a dangerous reaction from occurring?

A
Keep all sparks or flames away from the reactants.
B
Keep the reactants in separate containers.
C
Store the reactants together at a low temperature.
D
Store the reactants together at a low pressure.
8

Which statement defines calorimetry?

A
a device that is used to measure the heat that is gained or lost during a chemical change
B
a unit of energy that is used when calculating energy exchange
C
the conservation of energy
D
the measurement of energy that is given off or absorbed in a physical or chemical process
9

What happens as the activation energy increases?

A
The reactant surface area decreases.
B
The pressure of the system decreases.
C
The kinetic energy of colliding molecules changes.
D
The reaction begins to slow down.
10

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 slower molecules to faster molecules when they are near.
C
Heat flows from faster molecules to slower molecules when they collide.
D
Heat flows from faster molecules to slower molecules when they are near.
11

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 from the metal to the water and calorimeter until they are all at room temperature.
B
Energy transfers to the metal from the water and calorimeter until they all reach a single temperature.
C
Energy transfers from the metal to the water and calorimeter until they all reach a single temperature.
D
Energy transfers to the metal from the water and calorimeter until they are all at room temperature.
12

Reactant cap p contains 50 cap j of energy, and reactant cap q contains 35 point 3 cap j of energy. The reactants combine to form product PQ , which contains 104 cap j of energy. What is the energy transformation?

A
Energy is absorbed because the product has more energy than the reactants have.
B
Energy is lost because the product has less energy than the reactants have.
C
Energy is lost because the product has more energy than the reactants have.
D
Energy is absorbed because the product has less energy than the reactants have.
13

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
kinetic energy into potential energy
B
potential energy into chemical energy
C
kinetic energy into electromagnetic energy
D
chemical energy into thermal energy
14

Which reaction is endothermic?

A
2 Na plus Cl sub 2 rightarrow 2 NaCl plus energy
B
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
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
HCl plus NaOH rightarrow NaCl plus cap h sub 2 cap o plus 58 kJ
15

Which describes the enthalpy change associated with an endothermic reaction?

A
It is positive 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 negative because the enthalpy of the reactants is greater than the enthalpy of the products.
D
It is positive because the enthalpy of the products is greater than the enthalpy of the reactants.
16

Which energy graph represents the nonspontaneous transition of graphite into diamond?

A
Image with description A graph with reaction progression on the horizontal axis and energy on the vertical axis. A line starts midway up the vertical axis, runs briefly parallel to the horizontal axis, slopes up a moderate amount, then curves down sharply to level out below the initial starting point.
B
Image with description A graph with reaction progression on the horizontal axis and energy on the vertical axis. A line starts midway up the vertical axis, runs briefly parallel to the horizontal axis, slopes up a small amount, then curves down to level out below the initial starting point.
C
Image with description A graph with reaction progression on the horizontal axis and energy on the vertical axis. A line starts midway up the vertical axis, runs briefly parallel to the horizontal axis, slopes up sharply, curves down sharply, and levels out below the initial starting point.
D
Image with description A graph with Reaction progression on the horizontal axis and energy on the vertical axis. A line starts low on the vertical axis, runs briefly parallel to the horizontal axis, slopes up sharply, curves down a short distance, and levels out.
17

Which statement about enthalpy is true?

A
The enthalpy of formation for a pure element in its standard state is always negative.
B
Enthalpy is not a state function because its change depends on the identities of the reactants and products.
C
Enthalpy is a state function because its change depends only on initial and final conditions.
D
The enthalpy of formation for a pure element in its standard state is always positive.
18

Butane cap c sub 4 cap h sub 10 g , Δ⁢H_f=−125.7 , combusts in the presence of oxygen to form CO sub 2 times g , Δ⁢H_f=−393.5kJ/mol , and cap h sub 2 cap o g , Δ⁢H_f=−241.82 in the reaction: 2 cap c sub 4 cap h sub 10 g plus 13 cap o sub 2 g rightarrow 8 CO sub 2 g plus 10 cap h sub 2 cap o g What is the enthalpy of combustion, per mole, of butane? 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
5314 point 8 kJ over mol
B
2 comma 657 point 4 kJ over mol
C
negative 2 comma 657 point 4 kJ over mol
D
negative 5314 point 8 kJ over mol
19

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

A
a car of a roller coaster moving quickly down a slope
B
a pot of boiling water on a gas stove
C
a patient receiving an X-ray in a hospital
D
a car burning gasoline to power the engine
20

Which best describes heat?

A
energy that decreases as a car slows to a stop
B
energy that is carried by electric and magnetic fields
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

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