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Subject:ChemistryPrice: Bought3
1. 2.00 mol of an element, burned in a calorimeter, raises the temperature of 200 g of water 10.0 oC. (specific heat capacity of water = 4.18 kJ/kg. oC). Calculate the molar heat of combustion for this element. (3)
2. Given the following equations calculate the enthalpy of reaction for 1 mole of hydroquinone C6H4O2(g) (4)
Use Hess' law.
C6H4(OH)2(aq) + H2O2(aq) à C6H4O2(aq) + 2H2O(l)
C6H4(OH)2(aq) à C6H4O2(aq) + H2(g) DHo = +177.4 Kj/mol
H2(g) + O2(g) à H2O2(aq) DHo = -191.2 Kj/mol
H2(g) + 1/2O2(g) à H2O(l) DHo = -241.8 Kj/mol
3. Baking soda thrown on a grease fire will decompose in the following manner.
2NaHCO3(s) → Na2CO3(s) + CO2(g) + H2O(l)
Use the following heats of formation of the various products and reactants in the above equation to find the overall heat of formation ?Hf for the overall reaction. (4)
?Hf 2NaHCO3(s) = -948 kJ/mol ?Hf Na2CO3(s) = -1131 KJ/mol
?Hf H2O(l) = -188 kJ/mol ?Hf CO2(g) = -394 kJ/mol
4. Calculate the voltage of the cell given the following standard reduction potentials of Fe and Mn and write the overall cell as a spontaneous reaction: (4)
Fe2+ + 2e- → Fe(s) Eo = -0.44 V
Mn2+ + 2e- → Mn(s) Eo = -1.18 V
5. Ka = 5.0 X 10-10 for formic acid, CHOOH. Given an initial 0.20 mol/L solution of formic acid calculate the following values at equilibrium (7):
CHOOH(aq) + H2O(aq) ⇔ H3O+ (aq) + CHOO- (aq)
a) [H+] (4)
b) pH (2)
c) pOH (2)
d) Kb (2)
