Chem notes

Calorimetry

1. How many calories would it take to raise the temperature of 200 g of water 100oC?

2. It takes 23.5 J to raise the temperature of 10.0 g of silver by 10oC. What is the specific heat of silver?

3. A 255 g quantity of gold is heated from 28oC to 100oC. How many joules of energy were used? (specific heat of gold = 0.13 J/goC)

4. What will be the final temperature of 5.00 g of silver at 37oC if it gives off 25.0 J of heat to the surroundings? (use specific heat from #2)

5. If 1.80 g of octane (C8H18) is burned in a bomb calorimeter and the temperature increased from 21.36 o C to 28.78 oC, what is the heat of combustion of 1 gram? 1 mole? (heat capacity = 11.66 kJ/C)

Thermochemistry

1. What is the heat capacity of mercury if it requires 167 J to change the termperature of 15.0 g mercury from 25.0 oC to 33.0 o C?

2. Consider the reaction: C2H5OH (l) + 3O2 (g)  2CO2 (g) + H2O H = -1.37 x 103 kJ

When a 15.1 g sample of ethanol is burned, how much energy is released as heat?

3. When 0.157 mole NH3 is reacted with excess HCl, 6.91 kJ of energy is released as heat. What is the H for this reaction per mole of NH3 consumed?

4. Calculate the H for the following reactions using Hf
a. Fe2O3 (s) + 3CO(g)  3CO2 (g) + 2 Fe(s)

b. CaO(s) + CO2 (g) CaCO3 (s)

5. Calculate the H for the reaction: ClF + F2  ClF3

Given: 2ClF + O2 Cl2O + F2O H= 167.4 kJ 2ClF3 + 2 O2 Cl2O + 3F2O H= 341.4 kJ

2F2 + O2 2F2O H= -43.4 kJ

Hess’s Law and Heat of Formation
1. Given: S(s) + 3/2 O2 (g)  SO3 (g) H = -395.5 kJ
2SO2(g) + O2 (g) 2 SO3 (g) H = -198.2 kJ

Find H for: S(s) + O2 (g) SO2(g)

2. Given: O2 (g) + H2 (g) 2OH(g) H= 77.9 kJ
O2 (g)  2O(g) H = 495 kJ
H2 (g) 2H(g) H= 436 kJ Calculation H for: O (g) + H (g) OH(g)

3. Given: 2B(s) + 3/2 O2(g)  B2O3(g) H =-1273 kJ
B2H6(g) + 3 O2(g)  B2O3(g)+3H2O(g) H=-2035 kJ
½ O2 (g) + H2 (g) H2O(l) H=-286 kJ
H2O(l)  H2O(g) H=44 kJ
Calculate the enthalpy change for : 2B(s) + 3H2(g) B2H6(g)

4. Using the standard enthalpy of formation calculate the energy change for :
4NH3(g) + 7O2(g) 4NO2(g) + 6H2O(l)

5. Calculate the heat of formation of ClF3 (g) given:
2 ClF3 (g) + 2NH3(g)  N2(g) + 6HF(g) + Cl2(g) H=-1996 kJ

HESS’S LAW WORKSHEET
1. Use the thermochemical equations shown below to determine the enthalpy for the reaction:

2NH3(g) N2(g) + 3H2(g)
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2NO2(g) + 7H2(g) 2NH3(g) + 4H2O(l) ΔH°=256.5KJ

N2(g) + 2O2(g) 2NO2(g) ΔH°=-148.5KJ

H2O(l) H2(g) + 1/2O2(g) ΔH°=-78.7KJ

2. Use the thermochemical equations shown below to determine the enthalpy for the reaction:

H2CO + O2H2CO3
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H2CO3H2O + CO2 ΔH°=15.5KJ

Thermochemistry