Chem - Chapter 11 practice

The kinetic energy of gas particles is _____.

directly proportional to the square of the speed of the gas particles

By definition, the standard enthalpy of formation of a pure _______ in its standard state is equal to 0 kJ/mol.

element

Pressure is defined as the _______ exerted per unit of surface_______ .

force; area

A 10.0-gram mineral sample is heated to 80.0°C and immersed in a constant pressure calorimeter containing 50.0 grams of water (S water = 4.184 J/g⋅K) initially at 20.0°C. After heat exchange the temperature of the calorimeter is 30.0°C. Calculate the specific heat of the mineral (in J/g⋅K), assuming that all of the heat was exchanged with the water.

+4.18

Select all the statements that correctly describe the properties of gases. - Gases are much more compressible than liquids or solids. - Temperature changes have a large effect on the volume of a gas. - Gases have relatively low densities. - Gases mix with other gases only if their molecules are of the same type.

- Gases are much more compressible than liquids or solids. - Temperature changes have a large effect on the volume of a gas. - Gases have relatively low densities.

Select all the statements that correctly describe what happens when a gas is heated in a flexible container at constant pressure. - The gas increases in volume because the particles increase in size. - The gas particles collide with the walls of the container with a greater force. - The surface area of the walls of the container decreases. - The volume of the gas container increases. - The gas particles move faster.

- The gas particles collide with the walls of the container with a greater force. - The volume of the gas container increases. - The gas particles move faster.

Calculate the standard enthalpy change for the reaction SiO2 (s) + 4HF (g) → SiF4 (g) + 2H2O (l) given the information in the table below. Compound ΔH°f (kJ/mol) HF(g) -273.0 H2O(l) -285.8 SiF4(g) -1614.9 SiO2(s) -910.9

-183.6 kJ

A solid initially at 75°C is placed in an insulated water bath initially at 30°C. The temperature of the system reaches 45°C. The change in temperature of the solid was ______°C, and the change in temperature of the water bath was ______°C. Be careful with + and - signs!

-30; 15

Arrange the following gases in order of decreasing (fastest at the top, slowest at the bottom) diffusion rates. methane helium neon fluorine

1.Helium 2.Methane 3.Neon 4. Fluorine

Which of the following reactions is associated with the standard enthalpy of formation of NH3 (g)?

1/2N2 (g) + 3/2H2 (g) → NH3 (g)

Calculate ΔH°rxn for the reaction A + 2B → 2C using the ΔH°f values given below. Compound: ΔH°f: A a B b C c

2(c) - (a) - 2(b)

If an exothermic reaction heats a system with a total mass of 10 grams from 20°C to 30°C what is the total enthalpy change? Assume that the specific heat of the system is 2 J/g⋅K.

200J

Using Hess's law, select the manipulations to the given steps necessary to generate the overall chemical equation for the combustion of diamond to carbon monoxide (a difficult and expensive experiment). Select all that apply, including the correct overall equation. We are given the following thermochemical equations Eqn 1: C(graphite) + O2(g) → CO2(g) ΔH1 = -393.5 kJ Eqn 2: 2CO(g) + O2 (g) → 2CO2(g) ΔH2 = -566.0 kJ Eqn 3: C(diamond) → C(graphite) ΔH3 = -1.88 kJ

2C(graphite) + 2O2(g) → 2CO2(g) ΔH1' = 2ΔH1 = -(2)393.5 kJ = -787.0 kJ 2C(diamond) → 2C(graphite) ΔH3' = 2ΔH3 = -(2)1.88 kJ = -3.76 kJ Overall equation is 2C(diamond) + O2(g) → 2CO(g) ΔHrxn = -224.8 kJ 2CO2(g) → 2CO(g) + O2(g) ΔH2' = -ΔH2 = +566.0 kJ

Consider the following reactions: 2A → B; ΔH = x 2B → C; ΔH = y What is the total enthalpy change for the reaction 4A → C?

2x + y

Given that the specific heat of water is 4.184 J/g·°C, match the heat (left column) with the temperature change in °C (right column) for 10.0 g of water.

4.18 = 0.100 10.0 = 0.239 41.8 =1.00 418 = 10.0

Which pressure is the greatest? 760 psi 760 atm 760 Pa 760 torr 760 mmHg

760 atm

Select all the statements that correctly describe a gas contained in a rigid cylinder fitted with a moveable piston. Refer to the visual provided. - At the particulate level, the gas particles are pushed closer together as the piston moves down. - The gas may be compressed by decreasing the external pressure. - At the particulate level, the gas particles are forced farther apart as the piston moves down. - The gas may be compressed by increasing the external pressure.

At the particulate level, the gas particles are pushed closer together as the piston moves down. The gas may be compressed by increasing the external pressure.

Why does pressure rise as the volume of a piston filled with gas is reduced at constant temperature? Hint: Use a molecular view of gases to guide your reasoning.

Collisions with the walls are more frequent.

Select all of the statements that correctly describe bond enthalpies. Bond enthalpies are always positive. Bond enthalpies can be positive or negative Bond enthalpies represent the energy required to break bonds. Bond enthalpies are the energy generated when a bond is broken. Bond enthalpies are always negative.

Bond enthalpies are always positive. Bond enthalpies represent the energy required to break bonds.

Which of the following statements about effusion and diffusion are correct? - Both the effusion rate and the diffusion rate are inversely proportional to the square root of the molar mass of the gas. - The rate of effusion is exactly the same as the rate of diffusion for a given substance. - Lower molar mass gas particles effuse and diffuse faster because the urms is higher. - Diffusion and effusion are the same processes. The effusion rate is proportional to the density of a gas.

Both the effusion rate and the diffusion rate are inversely proportional to the square root of the molar mass of the gas. Lower molar mass gas particles effuse and diffuse faster because the Urms is higher.

_____ is the measurement of heat changes.

Calorimetry

Which of the following is the best definition of calorimetry?

Calorimetry is the measurement of heat changes that accompany physical or chemical processes.

Match each term describing the movement of gas molecules to its correct definition. Diffusion Effusion

Diffusion = Mixing of gases resulting from random motion Effusion = Escape of gas molecules from a container into a region of vacuum

Which of the following reactions would have an enthalpy change equal to ΔHf°? Select all that apply. 3O2 (g) → 2O3 (l) CH4 (g) → C(graphite) + 2H2 (g) Hg (s) + S (s) → HgS (s) Fe (s) + 3/2 Cl2 (g) → FeCl3 (s) C(graphite) + O2 (g) → CO2 (g)

Fe (s) + 3/2 Cl2 (g) → FeCl3 (s) C(graphite) + O2 (g) → CO2 (g)

How is pressure defined mathematically?

Force / Area

What are the relative rates of diffusion of helium and neon under identical conditions of temperature, pressure, and volume? Assume that helium has a molar mass of 4.0 g/mol, while neon has a molar mass of 20. g/mol.

Helium diffuses 2.2 times as fast as neon.

For a reaction that proceeds through a series of steps, ΔH overall = ΔH1 + ΔH2 + ΔH3 + .... This is a restatement of _______ law.

Hess'

Which of the following substances would have a standard enthalpy of formation equal to 0 kJ/mol? Select all that apply. Br2 (g) O3 (g) Hg (l) C (diamond) Ar (g) H2 (g)

Hg (l) Ar (g) H2 (g)

Consider the reaction shown. Select all the statements that correctly apply to the calculation of ΔH for this reaction using the bond energies provided.

In this reaction, two C-Cl bonds are formed. ΔH for this reaction is equal to -168 kJ/mol.

Using the general trends in the images provided, select all the statements that correctly describe the distribution of molecular speeds. - Most gas particles have speeds higher or lower than the most probable speed at a given T. - At the same T, the most probable speed of a He atom is greater than that of a H2 molecule. - For any gas, the most probable speed decreases as T increases. - SF6 molecules moves more slowly than SO2 molecules at the same T.

Most gas particles have speeds higher or lower than the most probable speed at a given T. SF6 molecules moves more slowly than SO2 molecules at the same T.

Select all the statements that describe the particles in a sample containing a mixture of gases at a given temperature. On average, the lighter particles move faster than the heavier particles. All the particles have the same most probable speed. All the particles have the same average kinetic energy. All the particles have the same mass.

On average, the lighter particles move faster than the heavier particles. All the particles have the same average kinetic energy.

The SI unit for pressure is the _____.

Pascal (Pa)

Which of the following factors determine whether a given substance exists as a solid, liquid, or gas? Select all that apply. Type of container Temperature Pressure

Temperature Pressure

Match each term with its correct units.

Specific heat = J/ g⋅°C Heat capacity = J/°C

Generate the equation A + 2B → 2D from a combination of the reactions provided. Reaction 1: A + 2B → 2C Reaction 2: C → D How must reactions 1 and 2 be combined to sum to the overall reaction?

Reaction 1 + 2(Reaction 2)

CO (g) can be produced by the reaction of coal with steam, as shown by the balanced equation: H2O (g) + C (s) → CO (g) + H2 (g). Which of the following options correctly reflect the steps required to calculate ΔH for this reaction, given the information shown below? Select all that apply. Reaction 1: H2 (g) + 1/2O2 (g) → H2O (g); ΔH = -242.0 kJ Reaction 2: 2CO (g) → 2C (s) + O2 (g); ΔH = +221.0 kJ

Reaction 2 must be reversed and divided by 2. ΔH = +131.5 kJ

Match the effects of the following combinations of Reactions 1 and 2 with the reaction resulting from these combinations. Reaction 1: A → 2C Reaction 2: C → B

Rxn 1 + (-Rxn 2) = A + B -> 3C Rxn 1 + 2(Rxn 2) = A -> 2B (-Rxn 1) + (-Rxn 2) = B + C -> A

Two solids of identical mass, A and B, are analyzed using identical calorimeters (containing the same amount of water, each at room temperature). When the solids are heated to the same initial temperature and placed in their calorimeters, the final temperature of solid A's calorimeter is higher than that of B. What can we infer from this?

S solid A > S solid B

The pressure in a gas arises because the particles of a gas strike each other and the walls of their container, exerting a(n)_______ . The greater the number of gas particles in a particular volume, the_______ the pressure within the gas.

force; greater

The standard enthalpy of ______ is the change in enthalpy associated with the chemical reaction that generates 1 mole of a substance from its constituent _______ in their standard states.

formation; elements

Which of the following are postulates of the kinetic molecular theory of gases? - The gas particles are in constant, random motion although they do move in straight lines. - The gas particles do not exert attractive or repulsive forces on each other. - Collision of gas particles are assumed to be elastic. - The volume of gas particles is negligible compared to the volume occupied by the gas. - The average kinetic energy of the gas particles is inversely proportional to the absolute temperature.

The gas particles are in constant, random motion although they do move in straight lines. The gas particles do not exert attractive or repulsive forces on each other. Collision of gas particles are assumed to be elastic. The volume of gas particles is negligible compared to the volume occupied by the gas.

How does a gas exert pressure? - The weight of the gas particles pressing on each other creates the pressure. - The moving gas particles strike each other and the walls of the container, exerting a force. - Pressure arises as the gas particles try to avoid contact with each other. - The gas particles repel each other, creating pressure.

The moving gas particles strike each other and the walls of the container, exerting a force.

Which of the following options correctly describe the procedure used to calculate ΔH for a reaction using bond energies? Select all that apply.

The sum ΔH bonds broken is given a positive value. ΔH for the reaction is given by (sum of ΔH bonds formed) + (sum of ΔH bonds broken)

The particles in a gas have a _____ distance between them than the particles of a liquid or a solid and their movement is random. Gas particles therefore move _____ freely than the particles of solids or liquids.

greater; more

Use the equation for specific heat to determine the function needed to solve for the variables associated with temperature change. (s = specific heat; q = heat)

heat = s × mass × ΔT mass of substance = q/s×ΔT change in temperature = q/mass×s specific heat = q/mass×ΔT

The root-mean-square (rms) speed of a gas is _____ proportional to the square root of its molar mass. H2 therefore has a _____ rms speed compared to O2 at the same temperature.

inversely, higher

Gases tend to have _____ densities than either liquids or solids, and their _____ change greatly with changes in temperature or pressure.

lower, volumes

Compare the molecular speeds for N2 at a constant temperature using the image provided. The greatest fraction of gas molecules with the most probable speed is observed at the _____ temperature.

lowest

The heat capacity of an object may be found using the specific heat of the composition of the object multiplied by the _____.

mass of the substance

A sample of a gas is compressible; i.e., its volume can be significantly decreased. This is because ______

particles in the gas phase are separated by relatively large distances.

An element that is in its most stable form at ordinary atmospheric pressure is in its ______ state (usually signified by a degree sign).

standard

Hess's law states that the enthalpy change for an overall process (which can be broken into multiple steps) will be equal to the _____ of the enthalpy changes of its individual steps.

sum

A salt is dissolved in a bath of water. Calculate the total amount of heat taken in or given out by the system (in J) if the temperature of mass of water grams of water decreases from Ti (°C) to Tf (°C) when mass of salt grams of salt is added to it. Assume the specific heat capacity of the solution is s J/g⋅K. (Hint: consider the total mass of the solution.)

s⋅(mass of water + mass of salt)⋅(Tf - Ti)

Which of the following parameters affect the root-mean-squared (rms) speed of a sample of a pure substance in the gas phase? temperature of the sample number of particles in the sample pressure of the sample molar mass of the substance

temperature of the sample molar mass of the substance

Select the answer that best completes the following sentence:The bond enthalpy is ______. - the enthalpy change associated with breaking a particular bond in one mole of gaseous molecules - the total enthalpy change when 1 mole of gaseous molecules is formed from its elements - the enthalpy change associated with forming a particular bond in one mole of gaseous molecules

the enthalpy change associated with breaking a particular bond in one mole of gaseous molecules

Select the answer that best completes the following sentence. The standard enthalpy of formation, ΔHf°, is ______.

the enthalpy change when one mole of a substance is formed from its constituent elements in their standard states

The root-mean-square (rms) speed (urms) of a gas particle is _____. (Select all that apply.) - the speed of gas particles that have the average kinetic energy - inversely proportional to the square root of the molar mass - proportional to the square root of the absolute temperature of the gas particles - the speed of all the gas particles in a given sample

the speed of gas particles that have the average kinetic energy inversely proportional to the square root of the molar mass proportional to the square root of the absolute temperature of the gas particles

Which equation correctly represents the effects of the absolute temperature and molar mass of the gas on the root-mean-square (rms) speed? ℳ denotes the molar mass of the gas.

urms = √3RT /ℳ

Consider the following reactions: A → 2B; ΔH = x kJ B → C; ΔH = y kJ What would be the enthalpy change associated with the reaction below? A → 2C

x + 2y

For the hypothetical reaction below, select the expression that would be equal to the enthalpy of the reaction. A-A + B-B → 2 A-B Bond Enthalpies: A-A = x B-B = y A-B = z

x + y - 2z

Select the correct form of the equation to find the enthalpy of a reaction from average bond enthalpies.

ΔH° = ΣBE(reactants) - ΣBE(products)

An unknown solid is placed in a freezer until it reaches a constant temperature. It is then placed in a room temperature water bath. Identify the sign (+/-) of the temperature change for the solid and for the water bath. Instructions

ΔT solid = Positive ΔT water bath = Negative