Bread – 44.5 38 41.25
Rice cake – 33 39 36
Cracker – 48 68 58
Crisps – 46 38 42
Kit Kat – 40 48 44
I have also measured the mass before and after the energy transfer:
Bread: – 0.3 0.32 w 0.31
Rice cake: – 0.23 0.15 0.19
Cracker: – 0.11 0.2 0.16
Crisps: – 0.14 0.01 0.08
Kit Kat: – 0.2 0.4 0.3
To work out the mass change we can subtract the average mass left from the original average mass:
Bread = 1.15 – 0.31 = 0.84
Rice cake = 1.9 – 0.19 = 1.71
Cracker: = 1.55 – 0.16 = 1.39
Crisps: = 1.04 – 0.08 = 0.96
Kit Kat: = 2.68 – 0.3 = 2.38
To calculate the amount of energy transferred to the water, we can use the formula
m x c x T where m = mass of water, c = specific heat capacity of water (0.004182) and T = the change in temperature:
Change in temperature:
Bread: 16.75
Chewy: 11.5
Cracker: 33.5
Crisps: 17.5
Kit Kat: 19.5
So:
Bread = 20 x 0.004182 x 16.75 =1.4 KJ transferred
Rice cake: = 20 x 0.004182 x 11.5 = 0.96 KJ transferred
Cracker: = 20 x 0.004182 x 33.5 = 2.86 KJ transferred
Crisps: = 20 x 0.004182 x 17.5 = 1.46 KJ transferred
Kit Kat: = 20 x 0.004182 x 19.5 = 1.63 KJ transferred
This means that:
0.84g of bread released 1.4 KJ of energy
1.71g of rice cakes released 0.96 KJ of energy
1.39g of crackers released 2.86 KJ of energy
0.96g of crisps released 1.46 KJ of energy
2.38g of Kit Kat released 1.63 KJ of energy
Now I will find the amount of energy released per gram of food:
Bread = 1.4/1.59 = 0.88 KJ released per gram of food
Rice cake: = 0.96/1.9 = 0.51 KJ released per gram of food
Cracker: = 2.86/1.55 = 1.85 KJ released per gram of food
Crisps: = 1.46/1.04 = 1.40 KJ released per gram of food
Kit Kat: = 1.63/2.68 = 0.61 KJ released per gram of food
Now I am going to compare these values with the energy values given:
Bread: 9.6 KJ
Rice cake: 3.2 KJ
Cracker: 7.4 KJ
Crisps: 18.7 KJ
Kit Kat: 22.2 KJ
As you can see, there are huge differences between the values that I have calculated and the values given; this could have been cause by a variety of problems:
- The energy could not have been entirely transferred to the water because some of it heated the surroundings
- Some of the items would not set alight quick enough before they were melted
Conclusion:
My results are not really what I expect, for example, I would have expected the Kit Kat to release the most energy because it contains the most fat, but it did not. Also, the cracker released a huge amount of energy which I do not think that it could have done.
Evaluation:
I think that my results are not very good, this is because there had been a lot of problems during the experiment; the rice cake fell apart and melted on the burning mat so it was impossible to measure the exact amount of energy given out, the crisps were hard to burn because they cracked when you tried to spear them on a mounted needle and a lot of the Kit Kat was melted in the hot flames of the Bunsen burner when I tried to get it alight. The other possible error could have been that when I changed the water, the boiling tube might have still been hot, so it would have warmed up the water before I even started to heat it
Possible improvements:
If I could have done this experiment again, I would have made a number of improvements:
- Use spoons to replace the mounted needle; so the rice cake and the crisps would not fall apart
- Use a smaller flame while trying to get the Kit Kat alight so it would not melt as quickly
- Use a new boiling tube every time for each different food to minimize the amount of heat that would be transferred from the boiling tube to the water.