A calorimeter was used to oxidise completely 2g of a food sample,causing a temperature rise of 5degrees C in 100cm3 of water(this figure includes the water equivalent of the apparatus).
How much energy was present in the food sample(in joule per g)?
To determine the amount of energy in the food sample, we need to calculate the heat absorbed by the water in the calorimeter. This heat absorbed is equal to the energy released during the combustion of the food sample.
First, we need to calculate the heat absorbed or released by the water using the formula:
Q = mcΔT
Where:
Q is the heat absorbed or released (in joules),
m is the mass of the water (in grams),
c is the specific heat capacity of water (4.18 J/g°C), and
ΔT is the change in temperature (in °C).
In this case, the mass of water used is 100g (100cm3 of water is approximately equal to 100g), and the change in temperature is 5°C.
Q = (100g) * (4.18 J/g°C) * (5°C)
Q = 2,090 J
Now, we need to subtract the water equivalent of the apparatus from the total heat absorbed by the water. The water equivalent is the mass of water that would absorb the same amount of heat as the apparatus for the given temperature change. Let's assume the water equivalent is 10g.
Total heat absorbed by the water + apparatus = Q + (water equivalent * specific heat capacity * ΔT)
Total heat absorbed by the water + apparatus = 2,090 J + (10g * 4.18 J/g°C * 5°C)
Total heat absorbed by the water + apparatus = 2,090 J + 209 J
Total heat absorbed by the water + apparatus = 2,299 J
Since the total heat absorbed by the water + apparatus is equal to the energy released during the combustion of the food sample, we can say that the food sample contained 2,299 J.
To calculate the energy per gram, we divide the total energy by the mass of the food sample used, which is 2g in this case:
Energy per gram = Total energy / Mass of food sample
Energy per gram = 2,299 J / 2g
Energy per gram ≈ 1,150 J/g
Therefore, the amount of energy present in the food sample is approximately 1,150 joules per gram.