A) When concentrated sulfuric acid is added to cold water, the temperature of the mixture rises. This indicates that heat is released from the reaction into the surroundings (the water). Therefore

a) When concentrated sulfuric acid is added to cold water, the temperature of the mixture rises. This indicates that heat is released from the reaction into the surroundings (the water). Therefore, the process is exothermic.

The student's answer is incorrect.

• Exothermic
• Reason: The temperature of the mixture rises because heat energy is released from the chemical process into the surroundings.

b)

• (i) The activation energy of the uncatalysed reaction is the energy difference from the reactants to the highest peak. This is represented by letter A. The student's answer "D" is incorrect.
  • A
• (ii) The activation energy of the catalysed reaction is the energy difference from the reactants to the lower peak (the peak of the catalysed pathway). This is represented by letter D. The student's answer "A" is incorrect.
  • D
• (iii) The enthalpy change of reaction ($\Delta H$) is the difference in energy between the products and the reactants. This is represented by letter E. The student's answer "E" is correct.
  • E

c) The given reaction is:

$$\text{C(g)} + \text{O}_2\text{(g)} \longrightarrow \text{CO}_2\text{(g)} \quad \Delta H = -394 \text{kJ/mol}$$

The enthalpy change ($\Delta H$) for the combustion of one mole of carbon is $-394 \text{kJ/mol}$. The negative sign indicates that the reaction is exothermic, meaning heat is released.
When one mole of carbon is burnt completely in oxygen, the amount of heat released is the magnitude of the enthalpy change.

Heat released $= |\Delta H|$
Heat released $= |-394 \text{ kJ/mol}|$
Heat released $= 394 \text{ kJ/mol}$

The student's answer "-394KJ" is incorrect because "released" already implies the negative sign.

• 394 kJ