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Which describes the enthalpy change associated with an endothermic reaction?

It is negative because the enthalpy of the products is greater than the enthalpy of the reactants.

It is positive because the enthalpy of the products is greater than the enthalpy of the reactants.

It is negative because the enthalpy of the reactants is greater than the enthalpy of the products.

It is positive because the enthalpy of the reactants is greater than the enthalpy of the products.

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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 .

–902 kJ

–104.6 kJ

104.6 kJ

900.8 kJ

Which direction does thermal energy flow in the following diagram?

Heat flows from the ice cream to the hand.

Heat flows from the hand to the ice cream.

The system is in a state of equilibrium.

The system is too cold for heat to move.

Which reaction is endothermic?

HCl + NaOH NaCl + H2O + 58 kJ

6CO2 + 12H2O + energy C6H12O6 + 6O2 + 6H2O

2Na + Cl2 2NaCl + energy

2C2H6 + 7O2 4CO2 + 6H2O + 2,502 kJ

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?

chemical energy into thermal energy

kinetic energy into potential energy

kinetic energy into electromagnetic energy

potential energy into chemical energy

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

a pot of boiling water on a gas stove

a patient receiving an X-ray in a hospital

a car burning gasoline to power the engine

a car of a roller coaster moving quickly down a slope

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 .

60.00 kJ

61.05 kJ

63.09 kJ

68.60 kJ

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?

Energy transfers to the metal from the water and calorimeter until they are all at room temperature.

Energy transfers from the metal to the water and calorimeter until they are all at room temperature.

Energy transfers to the metal from the water and calorimeter until they all reach a single temperature.

Energy transfers from the metal to the water and calorimeter until they all reach a single temperature.

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

the size of the atoms in a substance

the number of molecules in a substance

the position of the electrons on the outer valence shells

the balance between intermolecular forces and kinetic energy

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

A bomb calorimeter is 10 times larger but works the same way.

A bomb calorimeter measures heat for liquid products only.

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.

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.

Which statement about enthalpy is true?

The enthalpy of formation for a pure element in its standard state is always positive.

The enthalpy of formation for a pure element in its standard state is always negative.

Enthalpy is a state function because its change depends only on initial and final conditions.

Enthalpy is not a state function because its change depends on the identities of the reactants and products.

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

Heat flows from faster molecules to slower molecules when they are near.

Heat flows from faster molecules to slower molecules when they collide.

Heat flows from slower molecules to faster molecules when they are near.

Heat flows from slower molecules to faster molecules when they collide.

How should the baking of a pizza be categorized?

as an exothermic process because the dough releases heat

as an endothermic process because the dough releases heat

as an exothermic process because the dough absorbs heat

as an endothermic process because the dough absorbs heat

Which best describes heat?

energy that is carried by electric and magnetic fields

energy that decreases as a car slows to a stop

energy that increases as a book is lifted to a higher shelf

energy that flows from a hot mug of tea to a cold hand

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 .

19.2°C

25.8°C

34.2°C

72.3°C

Which statement defines calorimetry?

the conservation of energy

a unit of energy that is used when calculating energy exchange

a device that is used to measure the heat that is gained or lost during a chemical change

the measurement of energy that is given off or absorbed in a physical or chemical process

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?

Energy was created inside the blocks.

Energy was destroyed inside the blocks.

Energy was absorbed into the blocks from outside the system.

Energy was transferred from the warmer block to the cooler block.

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 .

13.5 kJ of energy released

13.5 kJ of energy absorbed

84.6 kJ of energy released

84.6 kJ of energy absorbed

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 .

2,747.7 cal/mol

2,771.8 cal/mol

2,811.7 cal/mol

3,280.0 cal/mol

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

Kinetic energy increases during exothermic changes and decreases during endothermic changes.

Kinetic energy decreases during exothermic changes and increases during endothermic changes.

Kinetic energy does not change, but the potential energy does.

Kinetic energy changes in the opposite way that the potential energy changes.

An engineer wants to determine an efficient method for condensing large amounts of steam into liquid water. Which constant should she use?

Hfus

–Hvap

Hvap

–Hfus

Which statement about exothermic reactions is accurate?

As reactants form products, the potential energy decreases.

As reactants form products, the potential energy increases.

Thermal energy is transferred from the product to the reacting substances.

Thermal energy is transferred from the surroundings to the reacting substances.

The enthalpy of formation for C6 H6 (I) is 49.0 kJ/mol. Consider the following reaction.Is the reaction endothermic or exothermic, and what is the enthalpy of reaction? Use .

exothermic; Hrxn = 49.0 kJ

exothermic; Hrxn = –49.0 kJ

endothermic; Hrxn = 49.0 kJ

endothermic; Hrxn = –49.0 kJ

The molar heat of vaporization for methane, CH4, is 8.53 kJ/mol. How much energy is absorbed when 54.8 g of methane vaporizes at its boiling point?Use .

6.42 kJ

29.1 kJ

137 kJ

467 kJ

What scientific tool would be the most helpful when measuring the temperature of a substance that is undergoing a phase change?

a spectrophotometer

a thermometer

the periodic table

a scale

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