Chapter 7

The enthalpy change for the reaction of titanium metal with gaseous iodine is given by the following thermochemical equation: 2 Ti(s) + 3 I2(g) → 2 TiI3(s) ΔHrxn = −839 kJ What is the enthalpy change for the reaction below? TiI3(s) → Ti(s) + 3/2 I2(g)

+4.20 × 102 kJ

Determine the work done in L ⋅ atm when a sample of gas expands from 1.00 L to 2.50 L against an external pressure of 0.750 atm.

-1.13 L * atm

Determine the work done in L ⋅ atm when a sample of gas expands from 1.00 L to 2.50 L against an external pressure of 0.750 atm.

-1.13 L*atm

Calculate the change in internal energy (ΔE) for a system that is giving off 25.0 kJ of heat and is changing from 22.00 L to 19.00 L in volume at 1.50 atm pressure. (Remember that 101.3 J = 1 L ⋅⋅ atm)

-24.5 kJ

The enthalpy for the formation of 1 mole of NH3(aq) is -80.29 kJ/mol. What is the enthalpy for the formation of 3 moles of NH3(aq)?

-240.87 kJ

The specific heat capacity of liquid water is 4.18 J/g-K. How many joules of heat are needed to raise the temperature of 7.25 g of water from 22.0°C to 57.0°C?

1.06 × 10^3 J

A sample of copper absorbs 43.6 kJ of heat, resulting in a temperature rise of 60.0°C, determine the mass (in kg) of the copper sample if the specific heat capacity of copper is 0.385 J/g°C.

1.89 kg

A 4.50-g sample of copper metal at 25.0°C is heated by the addition of 133 J of energy. The final temperature of the copper is ________°C. The specific heat capacity of copper is 0.38 J/gK.

103

The specific heat capacity of methane gas is 2.20 J/g-K. How many joules of heat are needed to raise the temperature of 5.00 g of methane from 15.0°C to 36.5°C?

237 J

Which of the following equations describes the formation of a compound from its elements in their standard states? 2CH4(g)+4O2(g)→2CO2(g)+4H2O(l) 2NH3(g)→N2(g)+3H2(g) 2H2(g)+O2(g)→2H2O(l) N2O(g)+4H2(g)→2NH3(g)+H2O(l)

2H2(g)+O2(g)->2H2O(l)

What mass of butane in grams is necessary to produce 1.5×103 kJ1.5×103 kJ of heat? What mass of CO2CO2 is produced? C4H10(g)+13/2O2(g)→4CO2(g)+5H2O(g),ΔHrxn=−2658 kJ

33g , 99g mC4H10mCO2==−1.5×103 kJ−1.5×103 kJ××1 mol C4H10−2658 kJ4 mol CO2−2658 kJ××58.12 g1 mol C4H1044.01 g1 mol CO2

How much heat in joules will it take to raise the temperature of a 100.0 g piece of copper from 18°C to 35°C? The specific heat capacity of copper is 0.385 J ⁄ g · °C.

6.5 * 10^2 J

Consider this combination reaction: 2Mg(s)+O2(g)→2MgO(s) ΔH=−1204 kJ What is the enthalpy for the decomposition of 1 mole of MgO(s) into Mg(s) and O2(g)?

602 kJ/mol

What is a state function? Provide examples

A state function is a function whose value depends only on the state of the system, not on how the system arrived at that state. Exs) Pressure, Volume, Internal Energy

Define chemical energy.

Chemical energy is the energy associated with the relative positions of electrons and nuclei in atoms and molecules.

Under what conditions is the change in internal energy, ΔErxn , equal to the heat evolved in a chemical reaction?

Constant Volume

To determine whether a shiny gold-colored rock is actually gold, a chemistry student decides to measure its heat capacity. She first weighs the rock and finds it has a mass of 4.7 gg. She then finds that upon absorption of 52.7 JJ of heat, the temperature of the rock rises from 25 ∘C∘C to 57 ∘C∘C. Find the specific heat capacity of the substance composing the rock.

Cs = q/mΔT =(52.7 J)/(4.7 g)(57∘C−25°C) =0.35 J/g°C

Deviations from the ideal gas law are observed at high pressure and low temperature. Explain this in light of kinetic molecular theory.

Gases behave ideally when both of the following are true: (1) The volume of gas particles is small compared to the space between them. (2) The forces between the gas particles are not significant. At high pressures, the number of molecules increases, so the volume of the gas particles is much greater; and because the spacing btwn the particles is much smaller, the interactions become more significant. At low temps, the molecules are not moving as fast as at high temps, so that when they collide, they have a greater opportunity to interact.

Which 10.0 gg cube of metal at 65 ∘∘ CC, when added to 30.0 gg water at 25 ∘∘ CC, will result in the least temperature rise for water?

Gold

Identify the gas particle that travels the fastest. Ar H2 O2 Cl2 Xe

H2 (least)

Identify the element or molecule that has the highest effusion rate. He HCl Kr N2 Cl2

He

Which of the following gases has the highest average speed at 400K? N2O4 He ClO2 Xe

He

Which of the following samples will have the greatest average speed at 355 K? C2H4 Kr F2 He All of these samples will have the same average speed at the same temperature.

He

If the enthalpy change of a reaction in a flask is ΔH = +67 kJΔH = +67 kJ, what can be said about the reaction?

Heat is transferred from the surroundings to the reaction flask.

Give the units of specific heat capacity.

J/g K or J/g°C

Identify the element or molecule that has the lowest effusion rate. O2 H2 Kr CO2 SO2

Kr

Identify the gas particle that travels the slowest. Cl2 He Kr H2 SO2

Kr

Determine whether the sign of heat or work (relative to the system) is positive or negative. Gases push up a cylinder in a car engine. (Gases are the system.)

Negative (When gases push up a cylinder in a car engine work is done by the system. Therefore work is negative.)

Determine whether the sign of heat or work (relative to the system) is positive or negative.Steam condenses on skin, causing a burn. (The condensing steam is the system.)

Negative (When steam condenses on skin, causing a burn the system loses thermal energy. Therefore heat is negative.)

Determine whether the sign of heat or work (relative to the system) is positive or negative.An ice cube melts and cools the surrounding beverage. (The ice cube is the system.)

Positive (When the ice cube melts and cools the surrounding beverage the system gains thermal energy. Therefore heat is positive.)

A 55.0 gg aluminum block initially at 27.5 ∘C∘C absorbs 725 JJ of heat. What is the final temperature of the aluminum?

Tf=Ti+∆TTf=Ti+(q/mCs)=27.5°+(725°/(55g)(0.903J/g°C))=42.1°C

Calculate the enthalpy change for the following reaction: 2CO(g)+O2(g)→2CO2(g)2CO(g)+O2(g)→2CO2(g), ΔHrxn∘=?Δ�rxn∘=? Given the following enthalpies of formation: 2C(s,graphite)+O2(g)→2CO(g), ΔH1=−221.0kJ C(s,graphite)+O2(g)→CO2(g), ΔH2=−393.5kJ

The first reaction must be reversed, changing the sign of the ΔH1 value, and then the second equation needs to be multiplied by 2, changing ΔH2 ΔHrxn∘=2×ΔH2−ΔH1 =2×(−221.0kJ)−(−393.5kJ) =−566.0kJ

Which of the following statements is FALSE? -At very high pressures, a gas will occupy a larger volume than predicted by the ideal gas law. -Particles of different masses have different average speeds at a given temperature. -The larger a molecule, the faster it will effuse. -For a given gas, the higher the temperature, the faster it will effuse. -None of the above statements is false.

The larger a molecule, the faster it will effuse

When HCl(aq)HCl(aq) and NaOH(aq)NaOH(aq) are mixed in a beaker, the beaker feels warm to the touch. What is known about the enthalpy of this reaction?

The reaction is exothermic

Determine whether the specific heat capacity calculated in Part A is consistent with the rock being pure gold by referring to the table below. Substance Specific heat capacity, Cs(J/(g⋅∘C))∗(J/(g⋅∘C))∗ Elements: Lead0.128 Gold0.128 Silver0.235 Copper0.385 Iron0.449 Aluminum0.903 Compounds: Ethanol2.42 Water4.18 Materials: Glass (Pyrex)0.75 Granite0.79 Sand 0.84 ∗∗ At 298 KK.

The specific heat capacity of gold is 0.128 J/(g⋅∘C)J/(g⋅∘C); therefore, the rock cannot be pure gold.

For a certain process, q and w are both negative. Which description below best describes what happened during this process?

The system lost heat and did work on the surroundings.

The additional energy in a beaker of hot water compared to an otherwise identical beaker of room temperature water is ________.

Thermal Energy

Water being turned into ice cubes in a freezer is an example of _____.

an exothermic process and the change in enthalpy, deltaH, will be a negative number

Water being turned into ice cubes in a freezer is an example of _____.

an exothermic process, and the change in enthalpy, ΔH, will be a negative number

Ammonia reacts with oxygen according to the equation: 4NH3(g)+5O2(g)→4NO(g)+6H2O(g),ΔHrxn=−906 kJ Calculate the heat (in kJ) associated with the complete reaction of 155 gg of NH3NH3.

heat =−2.06×103kJ

What are the expected signs of ΔEsys and ΔEsurr?

ΔEsys is negative and ΔEsurr is positive.

Using the standard enthalpies of formation found in the textbook, determine the enthalpy change for the combustion of ethanol C2H5OH as given below.C2H5OH (l) + 3 O2(g) → 2 CO2(g) + 3 H2O(g)

−1234.8 kJ

In a coffee-cup calorimeter experiment, 10.00 g of a soluble ionic compound was added to the calorimeter containing 75.0 g H2O initially at 23.2°C. The final temperature of the solution was 31.8°C. What was the change in enthalpy for the dissolution of this compound? Give your answer in units of joules per gram of compound. Assume that the specific heat of the solution is the same as that of pure water, 4.18 J ⁄ g ⋅ °C

−3.1 × 102 J ⁄ g compound

What will be the change in enthalpy when 100.0 g of butane, C4H10, is burned in oxygen as shown in the thermochemical equation below?2 C4H10(l) + 13 O2(g) → 8 CO2(g) + 10 H2O(g) ΔH rxn = −5271 kJ

−4534 kJ