One tablespoon of peanut butter has a mass of 15g. it is combusted in a calorimeter whose heat capacity is 130 kj/degrees c. the temperature of the calorimeter rises from 22.4 degrees c to 25.2 degrees c. find the food caloric content of peanut butter (answer in cal/g).

5.794 Food Cal/g or 5796 cal/g

Explanation:

If we consider that we have an adiabatic system (there is no transfer heat between the system and its surroundings) we can say that the energy lost by the peanut butter was the energy win for the combusted calorimeter and this can be seen in a temperature rise. Taking this into account we can say:

Q_cal = Q_peanutbutter

Q_cal=C*ΔT  

Where  

C  is capacity in the combusted calorimeter (130 kJ/°C)

ΔT = 25.2-22.4 = 2.8 °C

Q_cal = 364 kJ = Q_peanutbutter

364kJ/15g =24.26 kJ/g  

24.26 KJ/g * 1000 J/1kJ = 24260 J/g  

24260 J/g * 1 Cal/4.1868J = 5794.40 Cal/g

If 1 food calorie = 1 Kcal  

The answer is 5.794 Food Cal/g or 5.794 Kcal/g