11/15 chem

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 (swater = 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

Calculate the standard enthalpy change for the reaction SiO2 (s) + 4HF (g) → SiF4 (g) + 2H2O (l) given the information in the table below.

-183.6 kJ

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

-30 +15

As the temperature of a gas increases _____. (Select all the options that complete this sentence correctly.)

-the average kinetic energy of the gas particles increase-the average speed of a gas particle increases

Which of the following are equivalent to 652 mmHg? Select all that apply.

0.858 atm 86.9 kPa

Match each of the following pairs of pressures by converting correctly between the units.

1.23 atm- 935 mm hg 82.4kpa- 618 mmhg 1.62*10-3 atm- 1.23 torr

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

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

Given the following thermochemical equations: 3A → 2B; ΔH = x kJ C → B; ΔH = y kJ What is the total enthalpy change for the reaction: 3232A → C?

1/2x-y

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

12N2 (g) + 32H2 (g) → NH3 (g)

Calculate ΔH°rxn for the reaction A + 2B → 2C using the ΔH°f values given below.

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

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

200 J

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

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

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

4.18 J- 0.100 c 10.0 j- 0.239 c 41.8 j- 1.00 c 418 j- 10.0 c

Which pressure is the greatest?

760 atm

Select all the statements that describe the particles in a sample containing a mixture of gases at a given temperature.

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

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 increasing the external pressure.

Select all of the statements that correctly describe bond enthalpies.

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. Lower molar mass gas particles effuse and diffuse faster because the urms is higher.

Which of the following reactions would have an enthalpy change equal to ΔHf°? Select all that apply.

C(graphite) + O2 (g) → CO2 (g) Fe (s) + 3232Cl2 (g) → FeCl3 (s)

_____ 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.

Which of the following are postulates of the kinetic molecular theory of gases?

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 gas particles do not exert attractive or repulsive forces on each other. The gas particles are in constant, random motion although they do move in straight lines.

At sea level, a cylindrical water column with a cross section of 1 cm2 has a mass of 1.03 kg. Select the correct values for the force and pressure exerted by this water column.

Force = 10.1 N Pressure = 1.01 × 105 Pa

A dining table with a mass of 45.3 kg has four cylindrical legs with diameters of 6.00 cm each. What is the force being exerted by the table on the floor, and what is the total pressure being exerted by the table on the floor?

Force = 444 N Pressure = 3.92 × 104 Pa

Which of the following substances would have a standard enthalpy of formation equal to 0 kJ/mol? Select all that apply.

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

Which molecules are gases at room temperature?

HCl NH3 CO2

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, ΔHoverall = ΔH1 + ΔH2 + ΔH3 + .... This is a restatement of _____ law.

Hess's

Select all the diatomic elements that exist as gases at room temperature.

Hydrogen gas Nitrogen and oxygen Halogens such as F2 and Cl2

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.

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)

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

Match each term with its correct units.

Specific heat- J/gc heat capacity- jc

Select all the statements that correctly describe the properties of gases.

Temperature changes have a large effect on the volume of a gas. Gases are much more compressible than liquids or solids. 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 particles move faster. The gas particles collide with the walls of the container with a greater force. The volume of the gas container increases.

Select the statement that correctly explains the source of the energy change in a chemical reaction.

The main contribution to ΔH is the difference in the bond energies of reactants and products.

Two tables that are equal in mass are resting on the same rug. The four legs of one table each have a 2" x 2" cross-section, while the four legs of the second table each have a 4" x 4" cross-section. Which table is exerting greater pressure on the rug?

The table with the thinner legs is exerting greater pressure.

Helium effuses 3.16 times faster than an unknown gas under identical conditions. Predict the identity of the unknown gas.

argon

Carefully view the attached images. The can collapses when the air in the container is removed using a vacuum pump because:

atmospheric pressure > pressure inside the can

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) + 12O2 (g) → H2O (g); ΔH = -242.0 kJ Reaction 2: 2CO (g) → 2C (s) + O2 (g); ΔH = +221.0 kJ

deltaH = +131.5 kJ reaction 2 must be reversed and divided by 2

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.

deltaT solid - positivedeltaT water bath - negative

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

diffusion- mixing effusion- escape

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

The atmosphere exerts a pressure on you; however, you do not feel the pressure and you are not crushed by it. This observation is explicable because the pressure inside your body is _____ the atmospheric pressure outside.

equal to

True or false: At the same temperature, the rms speed of H2 is twice that of O2.

false

Pressure is defined as the _____ exerted per unit of surface _____.

force, area

How is pressure defined mathematically?

force/area

The standard enthalpy of _____ 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

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- qs*ΔT change in temp- qmass*s specific heat-qmass*ΔT

When converting a pressure from units of atmosphere (atm) to millimeters of mercury (mmHg), the numeric value will _____.

increase

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

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

When converting a pressure from units of torr to millimeters of mercury (mmHg), the numeric value will _____.

not change

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.

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.

particles will collide more frequently with the walls of the container

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.

pressure temp

The enthalpy of a reaction may be calculated using average bond enthalpies using an equation in which the energy _____ bonds form is subtracted from the energy _____ break bonds.

released when; required to

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?

ssolid A > ssolid B

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

standard

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 water grams of water decreases from Ti (°C) to Tf (°C) when mass 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⋅(masswater + masssalt)⋅(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 molar mass of the substance

When walking on powdery snow, snowshoes keep you from sinking into the snow because _____. Remember, pressure is force per unit area.

the area of a snowshoe is greater than that of a boot

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

Select the answer that best completes the following sentence. The standard enthalpy of formation, ΔHfo, 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 proportional to the square root of the absolute temperature of the gas particles inversely proportional to the square root of the molar mass

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= square root of 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