1.)Which of the following statements is incorrect concerning the thermochemical

Question

1.)Which of the following statements is incorrect concerning the thermochemical equation below? 2SO3(g) 2SO2(g) + O2(g); H° = 198 kJ

For every mole of SO3(g) consumed, 99 kJ of heat at constant pressure is consumed as well. The reaction is endothermic. For the reaction 2SO2(g) + O2(g) 2SO3(g), H° = –198 kJ. The external pressure is 1 atm. The enthalpy of the reactants exceeds that of the products.

2.) What is the change in enthalpy when 4.00 mol of sulfur trioxide decomposes to sulfur dioxide and oxygen gas?
2SO2(g) + O2(g)    2SO3(g); H° = 198 kJ

3.)According to the following thermochemical equation, if 951.1 g of NO2 is produced, how much heat is released at constant pressure?
2NO(g) + O2(g)    2NO2(g); H° = –114.4 kJ

4.)How much heat is liberated at constant pressure when 58.5 g of calcium oxide reacts with 83.9 L of carbon dioxide gas, measured at 1.00 atm pressure and 25.0°C? (R = 0.0821 L • atm/(K • mol))
CaO(s) + CO2(g)    CaCO3(s); H° = –178.3 kJ

Explanation / Answer

1) Incorrect statement

The enthalpy of reactants exceeds that of the product

2) Change in enthalpy dH = -198 x 4/2 = -396 kJ

3) moles of NO2 = 951.1 g/46 g/mol = 20.67 mol

Heat released = -114.4 x 20.67/2 = -1182.32 kJ

4) moles of CaO = 58.5 g/56.08 g/mol = 1.04 mol

moles of CO2 = 1 x 83.9/0.0821 x 298 = 3.43 mol

Limiting reactant = CaO

Heat liberated = -178.3 x 1.04 = -185.43 kJ

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