A field kitchen uses propane cylinders to heat water for an expedition. Before choosing a cylinder, a student burns a measured mass of propane beneath a met...
Question 1 Report
A field kitchen uses propane cylinders to heat water for an expedition. Before choosing a cylinder, a student burns a measured mass of propane beneath a metal pan containing water. The displayed formula in Fig. 1 is for propane. Table 1 gives results from one trial. Some energy is transferred to the pan and the air rather than to the water.
| measurement | value |
|---|---|
| mass of water | 500 g |
| initial temperature of water | 18.0 degrees C |
| final temperature of water | 46.0 degrees C |
| mass of propane burned | 1.20 g |
(a) Give the molecular formula of propane. [1]
(b) Name the two products formed when propane burns completely in excess oxygen. [2]
(c) Complete the balanced equation for this reaction.
C3H8 + 5O2 → 3CO2 + .............. [2]
(d) Calculate the temperature rise of the water. [1]
(e) Calculate the energy transferred to the water, in J. Use: energy = mass of water × 4.2 × temperature rise. [3]
(f) Explain why the energy calculated in part (e) is less than the total energy released by the propane reaction. [2]
Answer Details
(a) Propane has molecular formula C3H8. [1]
(b) Complete combustion in excess oxygen produces carbon dioxide and water. [2]
(c) \[\mathrm{C_3H_8+5O_2\rightarrow3CO_2+4H_2O}\]
The missing product is 4H2O. [2]
(d) \[46.0-18.0=28.0\degree\mathrm{C}\]
The temperature rise is 28.0 °C. [1]
(e) \[\text{energy}=500\text{ g}\times4.2\times28.0\degree\mathrm{C}=58800\text{ J}\]
The energy transferred to the water is 58 800 J. [3]
(f) Not all the energy from combustion heats the water: some heats the metal pan, and some is transferred to the surrounding air. Energy transfer from flame to pan and water is therefore incomplete. [2]
Download The App On Google Playstore
Everything you need to excel in your exams
