# 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?

#### 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),