Question

An exothermic reaction 86.5 kJ. How many kilocalories of energy are released?

Answer 1

Hint: Calorie is the energy required to heat one gram of water by one degree Celsius at one atmosphere pressure. We can express the energy in calorie or joule or kilojoule or kilocalorie. The relationship between calorie and joule is as follows.
1 calorie = 4.184 J

Complete answer:
- In the question it is given that the chemical reaction is exothermic and releases 86.5 kJ of energy.
- In the question it is asked to convert the given energy 86.5 kJ into kilocalories.
- Before going to do the conversion we should know the relationship between calories and joules.
- The relationship between kilocalories (kcal) and kilojoules is as follows.
1 calorie = 4.184 J
1000 calorie = 4184 J
1 kilocalorie = 4.184 kJ
- Divide both the sides with 4.184 to get the energy in kilojoules in terms of kilocalories.
1 kJ = 0.239 kcal.
- In the question it is given to calculate 86.5 kJ into kilocalories.
86.5 kJ = (0.239) (86.5) kcal
86.5 kJ = 20.7 kcal.
- Therefore 86.5 kJ is equal to 20.7 kcal of energy and it is going to be released in an exothermic reaction to the surroundings.

Note:
Endothermic chemical reaction absorbs energy to make the reaction happen. But in case of exothermic reaction energy is going to be released after completion of the chemical reaction to the surroundings in the form of heat or light.