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

1 Answer
Peter M.
May 9, 2017

1 kJ=0.239 kcal

86.5 kJ=86.5⋅0.239=20.7 kcal

Explanation:

This problem is just a unit conversion, so you need to know the definition of a calorie. A calorie is a unit of energy equal to 4.184 J. This is the energy required to heat up one gram of water by one degree celsius at a pressure of one atmosphere. If 1 cal = 4.184 J, then 1000 cal = 4184 J.
Therefore:

1 kcal=4.184 kJ

Divide both sides by 4.184 to get kJ in terms of kcal.

1 kJ=0.239 kcal

Now you have your conversion factor and just need to multiply both sides by 86.5.

1⋅86.5 kJ=0.239⋅86.5 kcal

86.5 kJ=20.7 kcal

Related questions
See all questions in Chemical Reactions and Equations
Impact of this question
16818 views around the world
You can reuse this answer
Creative Commons License