A student carries out an experiment to find the energy value of some food samples using the following method:
The student repeats this method for a potato chip, a cashew nut, and a crouton.
State two safety precautions that the student should take when carrying out this experiment.
The student records the mass of food and the change in water temperature. For each food sample, they calculate the energy released in joule (J\text{J}J) using this formula:
energy released in J=mass of water in g×temperature rise in ∘C×4.2 \text{energy released in J} = \text{mass of water in g} \times \text{temperature rise in } ^{\circ}\text{C} \times 4.2 energy released in J=mass of water in g×temperature rise in ∘C×4.2The table below shows their results:
| Food | Mass of food before burning (ggg) | Change in water temperature (∘C^{\circ}\text{C}∘C) | Energy released from food sample (J\text{J}J) | Energy released from food sample (J per g\text{J per g}J per g) |
|---|---|---|---|---|
| Potato chip | 0.3 | 6 | 630 | 2100 |
| Cashew nut | 0.2 | 8 | 4200 | |
| Crouton | 0.4 | 5 | 525 | 1312.5 |
Calculate the energy released in J\text{J}J from the sample of cashew nut. Show your working.
Explain why the student calculates the energy released in J per g\text{J per g}J per g rather than just comparing the total energy released in J\text{J}J.
The actual energy value stated on the cashew nut packaging is 23 000 J per g23\,000\text{ J per g}23000 J per g.
Suggest why there is a difference between the student's experimental value and the value stated on the packaging.
Describe two ways the student could modify the apparatus to make the experimental value closer to the value on the packaging.
