Question

A chemical reaction gives off 2,100 kJ of heat energy. About how many calories is this ?

Answer 1

Answer: 501900 calories.

Explanation:

Exothermic processes are those processes in which heat is released and endothermic processes are those processes in which heat is absorbed.

Standard units for heat measurement are Joules and calories wherein  

1 joule = 0.239 Calorie.

Now 1 kJ = 1000 Joules

Therefore 2100kJ = $2100\times1000=2100000Joules$

As 1 Jolule is equivalent to 0.239 calorie

2100000 Joules are equivalent to=$\frac{0.239}{1}\times 2100000= 501900calories$

Thus it is 501900 calories.

Answer 2

We have to convert 2100 kilojoule into calories.

2100 Kilojoule is equal to 500 Calories.

The chemical reaction gives off 2100 Kilojoule of heat energy which indicates that the reaction is exothermic in nature. Calorie and Kilojoule both are units of energy. We know, 1 calorie=4.2 kilojoule= 4.2 KJ. So 4.2 KJ is equal to 1 Calorie i.e, 4.2 KJ= 1 Calorie. So, to convert KJ to calorie, we have to divide the energy given in KJ by quantity 4.2. Hence, 2100 Kilojoule energy is equal to $\frac{1 X 2100}{4.2}$ Calorie= 500 Calories.