Question 9
Some fuel in a spirit burner is burned, and the heat produced is used to heat a container of water.
In this experiment:
The mass of water heated = m g
The temperature rise = y °C
The specific heat capacity of water = c J K–1 g–1
What is the amount of heat energy absorbed by the water?
(Total 1 mark)
Question 10
This question is about enthalpy changes.
(a) A student determined the enthalpy of combustion of cyclohexane (C6H12).
The student
- placed a pure sample of cyclohexane in a spirit burner
- placed the spirit burner under a beaker containing 50.0 g of water and ignited the cyclohexane
- extinguished the flame after a few minutes.
The results for the experiment are shown in Table 1.
The student determined from this experiment that the enthalpy of combustion of cyclohexane is –1216 kJ mol–1
Use the data to calculate the final temperature of the water in this experiment.
The specific heat capacity of water = 4.18 J K–1 g–1
The relative molecular mass (Mr) of cyclohexane = 84.0
(4)
(b) A data book value for the enthalpy of combustion of cyclohexane is –3920 kJ mol–1
The student concluded that the temperature rise recorded in the experiment was smaller than it should have been.
Suggest a practical reason for this.
(1)
(c) Table 2 gives some values of standard enthalpies of combustion (∆cH⦵).
Use the data in Table 2 to calculate the enthalpy change for the reaction represented by this equation
6 C(s) + 6 H2(g) → C6H12(l)
(3)
(Total 8 marks)