Chapter 13 - Learnsmart Pretest

These steps describe how to use standard enthalpies of formation and Hess's law to calculate the energy change for a reaction. Put them in order from the first step to the last step.

- Use thermochemical equations for enthalpies of formation that contain the substances found in the desired equation -Manipulate the known thermochemical equations so that the products, reactants, and coefficients will match the desired equations when they are added -Add the manipulated chemical equations and their correspondingly manipulated enthalpy changes. -Cancel the common terms and check that the answer matches the desired equation.

Place these steps in order so that they describe how a calorimeter is used to measure energy that is absorbed or released.

-A known mass of water is placed in an insulated chamber -The initial temperature of the water is recorded -The reaction takes place and either releases energy to the water or absorbs energy from the water -The water cools down or heats up accordingly -The final temperature of the water is recorded

Which are examples of common combustion reactions?

-Natural gas, which is mostly methane, is burned to produce heat to cook food -Gasoline fuels vehicles such as cars and boats -Glucose in the body is converted to carbon dioxide and water, releasing energy

Why do chemists need a theoretical way to determine enthalpy changes?

-Some reactions occur under conditions difficult to duplicate in a laboratory -Some reactions occur very, very slowly -For some reactions, it is impossible or impractical to use a calorimeter

These steps describe how to determine the specific heat of an unknown metal using a foam-cup calorimeter. Put them in order from the first to last step.

-put a known mass of water into the foam-cup calorimeter -determine the initial temperature of the water -take a sample of metal of known mass and heat it up -place the metal into water -once the temperature of the water stabilizes, record the temperature. -Use the temperature change data to calculate specific heat

The water in a calorimeter absorbed 355.3 J of heat when an unknown metal with a mass of 8.40 g cooled by 180.0 C. THe specific heat of the metal was ____ J/(g C). (to three significant figures)

0.235

Using a calorimeter, it was determined that a piece of metal with a mass of 2.50 g absorbed 134.7 J of heat when its temperature increased by 120.0 C. What is the specific heat of the metal?

0.449 J/(g C)

Which equations correctly represent the relationships among energy units?

1 J = 0.2390 cal 1 J = 239.0 kcal

A sample of silver with a mass of 1.00 g increases in temperature from 20.00 C to 28.00 C. Given that silver has a specific heat of 0.235 J/(g C), the quantity of heat absorbed is ____ J. (to three significant figures)

1.88

What is the main difference between one mole of glucose being burned in a bomb calorimeter and one mole of glucose being metabolized in the body via cellular respiration?

Cellular respiration consists of many complex steps, whereas combustion in a bomb calorimeter is essentially one step.

Which equation correctly shows how the enthalpy of reaction is related to the enthalpy of the reactants and products?

Change H rxn = H products -H reactants

Standard enthalpies of formation for compounds are measured experimentally by reacting the component elements in their ____ ____ and then determining the enthalpy change for the reaction.

Standard states

One ____ is equal to 4.184 J, and one Calorie is equal to 1 ____.

calorie, kilocalorie

An insulated device used for measuring the amount of heat absorbed or released during a chemical or physical process is called a(n) ____.

calorimeter

Chemists need a theoretical way to determine the enthalpy change of a reaction because for some reactions it is impossible or impractical to use a ____.

calorimeter

The heat content of a system at a constant temperature is its ____.

enthalpy

The amount of heat required to raise the temperature of one gram of a substance by one degree Celsius is the ____ ____ of that substance.

specific heat

Water can be used to harness the energy of the Sun by absorbing solar radiation and then circulating it through homes and businesses. Water is well suited to this use because of its high ____ ____.

specific heat

Standard enthalpies of formation for compounds are measured experimentally by reacting the component elements in their ____ ____ and then determining the enthalpy change for their reaction.

standard states

In thermochemistry, the system plus the surroundings is the ____.

universe

A milkshake contains 2.05 x 10^6 J of energy. How many nutritional Calories are in the milkshake? Recall that 1 cal = 4.184 J and 1 Calorie = 1 kcal

490 Calories

What is the term for the heat content of a system at constant pressure?

enthalpy

The change in enthalpy for a reaction is called the ____ of ____

enthalpy, reaction

Which equation correctly shows how the universe, system, and surroundings are related?

universe = system + surroundings

Which statements best summarize how a foam-cup calorimeter can be used to determine the specific heat of an unknown metal?

The metal is heated and placed in the water in the calorimeter. The temperature change of the water is recorded.

Which of these relationships are correct?

change H vap = -change H cond change H fus = -change H solid

The enthalpy of vaporization of a substance has an equal but opposite sign to its enthalpy of ____.

condensation

Heat flows from the surroundings to the system when a(n) ____ reaction takes place.

endothermic

It is impossible to know the total ____ content of a substance.

energy

The combustion reaction between ____ and ____ produces water and provides the energy to lift a space shuttle into space.

hydrogen, oxygen

The heat required to melt one mole of a solid substance is called its ____ ____ of ____

molar, enthalpy, fusion