AnswersECTC-AL-Chemistry BUnit Test

Unit Test — Unit test Answers

23 verified answers
1
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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
2
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Which describes the enthalpy change associated with an endothermic reaction?

A
It is negative because the enthalpy of the products is greater than the enthalpy of the reactants.
B
It is positive 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 reactants is greater than the enthalpy of the products.
3

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.
4

Consider the following enthalpy diagram:Which label shows the overall enthalpy change and is the reaction exothermic or endothermic?

Question illustration
A
A, exothermic.
B
B, exothermic.
C
C, endothermic.
D
D, endothermic.
5

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
6

A sample of iron (Fe) with a mass of 200.0 g releases 9,840 cal when it freezes at its freezing point. What is the molar heat of fusion for iron?Use .

Question illustration
A
2,747.7 cal/mol
B
2,771.8 cal/mol
C
2,811.7 cal/mol
D
3,280.0 cal/mol
7

Consider the following intermediate chemical equations.How will oxygen appear in the final chemical equation?

Question illustration
A
as a product
Option A
B
as a reactant
Option B
C
O(g) as a product
D
2O(g) as a reactant
8

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
9

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.
10

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.
11

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
12

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.
13

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.
14

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.
15

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.
16

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
17

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
18

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 releases heat
C
as an exothermic process because the dough absorbs heat
D
as an endothermic process because the dough absorbs heat
19

Which is the best example of how electromagnetic energy is used?

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

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.

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