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# Sample Physical Chemistry Problems

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1) Ca(s) + 2H20(l) Ca(OH)2(OH)2(aq) + H2(g)
75.0g of Ca(AW = 40.08) are reacted with 40.0 H20 (MW = 18.02) according to the above equation if 30.0 L of H2 (g)(MW = 2.016) are produced at 20 0C,Calculate the pressure of H2 gas.

2) Calculate the heat released when 84.5g of SO2 (MW = 64.07) are used up according to the following equation. 2 SO2(g) + O2(g) + O(g) 2SO2(g) â–²Ho = 99.1kJ

3) Calculate the â–²T for a 87.5 g piece of copper when one adds 2.1kJ of heat energy to that piece of cooper. Copper has a specific heat capacity of 0.385 J/g 0C.

4) Write the thermo chemical equation for the standard enthalpy of formation of solid ammonium chloride,NH4Cl,given that the reaction releases 314 kilojoules per mole of ammonium chloride.

5) In an instant cold pack(used to treat athletic injuries),50.0g of NH4NO3 is mixed with 125 g of H2O at an initial temperature of 25.00 0C.After the dissolving of the salt, the final temperature of the solution is 3.10 0C.
Calculate the enthalpy change for the dissolution of NH4NO3 in Kj/mol.Assume that the masses are addictive .Also ,assume that the heat capacity of the calorimeter is zero and the solution has specific heat of 4.18J/g 0C.

NH4NO3 (s) H20 NH4NO3 (aq)

6) Calculate the â–² H0 for this reaction 3 NO2 (g) + H20 (l) 2HNO3 (aq) + NO (g).

7) Typical atmospheric pressure on Mt.Everest (29,028 ft) is 235 mm Hg.Convert this pressure to atm and in Hg.

8) A 3.50 L flask contains 7.65 g methane (CH4 MW = 16.04) at 27 0C.Calculate the pressure (in atm) inside the flask.
9) A gas sample is heated from -100C to 57.0 0C and the volume is increased from 2.00 L to 4.5 L .If the initial pressure is 0.425 atm, calculate the new pressure of the gas.

10) A gas consist of only carbon and hydrogen has an empirical formula of CH3. The gas has a density of 3.32 g/L at 27.0 0 C and 739 mm Hg.
a) Calculate the molar mass of the gass
b) Determine the molecular formula of the gas

11) Calculate the â–²H for this reaction:

2 C(s) + H2 (g) C2H2(g)

Given the following data

C2H2(g) + 5/2 O2(g) 2CO2 (g) + H2O(l) â–²H = -1299.6 kJ

C (s) + O2 (g) CO2(g) â–² H = - 393.5 kJ
H2(g) + 1/2O2(g) H2O(l) â–² H = -285.9 kJ

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#### Solution Preview

Thank you.

1) Ca(s) + 2H20(l) Ca(OH)2(OH)2(aq) + H2(g)
75.0g of Ca(AW = 40.08) are reacted with 40.0 H20 (MW = 18.02) according to the above equation if 30.0 L of H2 (g)(MW = 2.016) are produced at 20 0C,Calculate the pressure of H2 gas.

SOLUTION:
Ca(s) + 2H20(l) -> Ca(OH)2(aq) + H2(g)

Mole Ca = 75 g Ca (1 mol Ca / 40.08 g)
Mole Ca = 1.87

Mole H2O = 40 g (1 mol H2O / 18.02 g)
Mole H2O = 2.22

Finding the limiting reagent:
mole quotient for Ca = 1.87 mol / 1 mol = 1.87
mole quotient for H2O = 2.22 mol / 2 mol = 1.11

Therefore, H2O is the limiting reagent.

Solving for mole H2 produced:
Mole H2 = 2.22 mol H2O (1 mol H2 / 2 mol H2O)
Mole H2 = 1.11

Solving for pressure of H2 gas:
PV = nRT
P = nRT / V
P = 1.11 mol (0.08206 L-atm/K.mol)(293 K) / 30 L
P = 0.8896 atm

2) Calculate the heat released when 84.5g of SO2 (MW = 64.07) are used up according to the following equation. 2 SO2(g) + O2(g) + O(g) 2SO2(g) â–²Ho = 99.1kJ

Mole SO2 = 84.5 g (1 mol / 64.07 g) = 1.32
99.1 kJ / 2 mol SO2 = x / 1.32 mol SO2
x = 65.41 kJ This is the amount of heat released when 84.5 g SO2 is used

3) Calculate the â–²T for a 87.5 g piece of copper when one adds 2.1kJ of heat energy to that piece of cooper. Copper has a specific heat capacity of 0.385 J/g 0C.

q = heat = msâ–²T

Where: m = mass of material
s = specific heat capacity
â–²T = change in temperature

2100 J = 87.5 g (0.385 J/g.0C)(â–²T)
â–²T = 2100 J / [87.5 g (0.385 ...

#### Solution Summary

This five page solution provides step-by-step explanations for a series of physical chemistry problems.

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