Chemistry

1. 1.

   Explain the sign of the enthalpy change when a reaction warms its surroundings at constant pressure.

   [3 marks] · no calculator
2. 2.

   Why does a catalyst not change the enthalpy change of a reaction, even when it makes the reaction faster?

   [3 marks] · no calculator
3. 3.

   A reaction heats 100 g of solution from 20.0 to 26.0 degrees C. Use c = 4.18 J g^-1 K^-1 and 0.0500 mol reacted. Neglect losses and calculate the molar reaction enthalpy.

   [3 marks]
4. 4.

   Given deltaHf(CO2) = -394, deltaHf(H2O(l)) = -286 and deltaHf(CH4) = -75 kJ mol^-1, calculate deltaH for CH4 + 2O2 -> CO2 + 2H2O(l).

   [3 marks]
5. 5.

   For a reaction deltaH = +40.0 kJ mol^-1 and deltaS = +100 J mol^-1 K^-1, assumed constant. Calculate the temperature above which deltaG is negative, and explain why this does not guarantee a fast reaction.

   [4 marks]
6. 6.

   A combustion calorimeter gives a less negative enthalpy than a reliable reference. Explain how incomplete combustion and heat loss each cause this, and propose a distinct improvement for each.

   [4 marks] · no calculator

Original, unofficial practice questions from SubjectScout — not official past-paper questions.