# Gases, Temperature, Current and Reactions

1) Calculate w and Delta E for the expansion of 20.0g of nitrogen gas from a volume of 30.0 L to a volume of 40.0 L at a constant 300.0K.

2) The density of ice at its normal freezing temperature is 0.917g/mL while that of liquid water at the same temperature is 0.9998 g/mL . If Delta H(fusion) of ice is 6.009 kJ/mol, what is Delta E(fusion).

3) The heat of fusion of potassium bromide is 20.9 kJ/mol. If the entropy of fusion of this compound is 20.5 J/K-mol, what is the melting point of this compound?

4) Calculate the Gibbs Free Energy of the combustion of acetylene to form carbon monoxide and liquid water at 25 degrees Celsius.

5) Calculate the value of the equilibrium constant at 25 degrees Celsius for the reaction.

2SO2(g) + O2 <==> 2 SO3

6) Write the diagram of a cell which utilizes the following reaction.

2Fe^2+(aq) + Cl2 (g) => 2 Fe^3+(aq) + 2Cl^1-

7) A voltage of 1.09 V at 25 degrees Celsius was obtained from the cell

Sn(s) | Sn^2+ (aq) || Ag^1+ (aq, 0.05 M) | Ag (s)

What was the molar concentration of Sn^2+ in the cell?

8) Calculate the standard molar free energy of formation of liquid water at 25 degrees Celsius. Use the standard reduction potentials for this calculation.

9) A solution of nickel sulfate was electrolyzed for 1.50 hours between inert electrodes. If 35.0 grams of nickel was plated out, what was the average current.

10) Some fragments of bone from an excavation in Egypt were found to have a ^14C radioactivity of 0.629 times that in the bones of living animals. How old are the fragments?

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#### Solution Preview

1) Calculate w and Delta E for the expansion of 20.0g of nitrogen gas from a volume of 30.0 L to a volume of 40.0 L at a constant 300.0K.

From the first Law of thermodynamics

Delta E = q + w, where q = heat, and w = work

For an isothermal process (carried out at constant temperature) on an ideal gas, E depends entirely upon temperature, and so Delta E = 0, and w = -q.

However, w = -nRTln(V2/V1), where n = moles of N2 (calculated by mass /molar mass) R = 8.314 J/Kmol, T = 300 K, V2 = 40 L and V1 = 30 L.

2) The density of ice at its normal freezing temperature is 0.917g/mL while that of liquid water at the same temperature is 0.9998 g/mL . If Delta H(fusion) of ice is 6.009 kJ/mol, what is Delta E(fusion). Using similar thermodynamic equations Delta E = qp + w = DeltaH - PextDeltaV?

qp is the definition of Delta H, and w is defined as the change involume against and external pressure,

w = -Pext(DeltaV)

The external pressure is assumed to be 1 atm which = 101.325 J

The densities of both water and ice need to be divided by the mass of one mole to find the volume in mL, but since they are both divided by the same number, a ratio will work just the same.

Volume of water (0.9998 g/mL)/(18 g/mol) * 1000 mL/L =

Volume of ice (0.917 g/mol)(18 g/mol) * 1000 mL/L =

Delta E = 6009 J - (101.325 J)(0.9998/0.917)

3) The heat of fusion of potassium bromide is 20.9 kJ/mol. If the ...

#### Solution Summary

This complete solution identifies steps and includes calculations and answers for (1) through (10),

Elements of Crystallizes in Body-Centered Cubic Lattice

Chapter 11

5. An element crystallizes in a body-centered cubic lattice. The edge of the unit cell is 2.98 , and the density of the crystal is 8.99 . Calculate the atomic weight of the element.

9. Calculate the minimum number of grams of propane, , that must be combusted to provide the energy necessary to convert 5.70 of ice at -18.0 to liquid water at 71.5 .

21. The vapor pressure of a volatile liquid can be determined by slowly bubbling a known volume of gas through it at a known temperature and pressure. In an experiment, 4.08 of gas is passed through 7.4972 of liquid benzene, , at 27.1 and atmospheric pressure. The liquid remaining after the experiment weighs 5.9261 . Assuming that the gas becomes saturated with benzene vapor and that the total gas volume and temperature remain constant, what is the vapor pressure of the benzene in torr?

Chapter 14

7. The activation energy of an uncatalyzed reaction is 91 . The addition of a catalyst lowers the activation energy to 52

A. Assuming that the collision factor remains the same, by what factor will the catalyst increase the rate of the reaction at 34 ?

B. Assuming that the collision factor remains the same, by what factor will the catalyst increase the rate of the reaction at 112 ?

12. Calculate the fraction of atoms in a sample of argon gas at 337 that have an energy of 12.3 or greater.

25. The decomposition of H2O2, H2O2 (aq) H2O (l) + ½ O2 (g), is a first-order reaction. At a particular temperature near room temperature, the rate constant equals 7.0×10−4 . Calculate the half-life at this temperature.

34. At 415 , decomposes in the gas phase, . If the reaction is first order with a half-life of 56.3 at this temperature, calculate the rate constant in .

Chapter 20

11. A solution is electrolyzed, using a current of 8.00 .

A. What mass of is plated out after 3.00 days?

B. What amperage is required to plate out 0.230 from a solution in a period of 7.30 ?

23. How many coulombs are required to plate a layer of chromium metal 0.29 thick on an auto bumper with a total area of 0.30 from a solution containing ? The density of chromium metal is 7.20 .

28. What current flow is required for this electroplating if the bumper is to be plated in 14.2 ?

32. If the external source has an emf of 6.6 and the electrolytic cell is 69 efficient, how much electrical power is expended to electroplate the bumper?

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