Answers SS - TX - Chemistry BWriting and Balancing Chemical Equations

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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

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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.

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.

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.

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 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

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

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

Cancel out CO because it appears as a reactant in one intermediate reaction and a product in the other intermediate reaction.

Add the two CO molecules together, and write them as reactants in the final chemical reaction.

Write CO only once as a reactant in the final chemical reaction.

Write CO as a reactant and a product in the final chemical reaction.

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

as a product

as a reactant

O(g) as a product

2O(g) as a reactant

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

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

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.

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 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.

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.

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?

Reverse the first equation, and change the sign of the enthalpy. Then, add.

Reverse the second equation, and change the sign of the enthalpy. Then, add.

Multiply the first equation by three, and triple the enthalpy. Then, add.

Divide the third equation by two, and double the enthalpy. Then, add.

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

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

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

A, exothermic.

B, exothermic.

C, endothermic.

D, endothermic.

Which statement is true for most chemical reactions?

An energy change occurs during the breaking and forming of bonds.

The internal energy of the system increases during a reaction.

Energy is released during the formation of reactants.

The enthalpy of the products is higher than the enthalpy of the reactants.

Consider the following intermediate chemical equations.When you combine the intermediate chemical equations, which substance do you cancel out?

Upper P upper C l subscript 3.

PCl

An arrow is fired at a target on a high wall. How does the energy change between the moment the arrow is fired and the moment it hits the target?

The potential energy and kinetic energy remain the same.

The potential energy decreases as kinetic energy increases.

The kinetic energy decreases as potential energy increases.

The kinetic energy remains at zero, but potential energy increases.

How does the potential-energy diagram for a reaction indicate whether the reaction is endothermic or exothermic?

An endothermic reaction has reactants that are lower in energy than products because energy is absorbed to form the products.

An endothermic reaction has reactants that are higher in energy than products because energy is released to form the products.

An exothermic reaction has reactants that are lower in energy than products because energy is released to form the products.

An exothermic reaction has reactants that are higher in energy than products because energy is absorbed to form the products.

What type of energy is the sum of an object’s potential and kinetic energy?

mechanical energy

electromagnetic energy

chemical energy

thermal energy

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