Question

1 kilocalorie =
A) $4.186\,J$
B) $4186\,J$
C) $41.86\,J$
D) $418.6\,J$

Answer 1

Hint: A calorie is a unit of energy defined as the amount of heat needed to raise a quantity of water by one degree of temperature. The joule is the unit of energy in the International System of Units. It is equal to the energy transferred to (or work done on) an object when a force of one Newton acts on that object in the direction of the force's motion through a distance of one meter.

Complete step by step answer:
As mentioned in the hint, the units of joules and calories are defined differently using different references of measurement.
The Joule is the SI unit of measurement of energy while the calorie is the amount of energy defined as the amount of heat needed to raise a quantity of water by one degree of temperature. Here heat and energy can be used interchangeably.
The calorie is designed specifically to measure the energy required to change the temperature of water by one degree Celsius at 1 standard atmosphere.
The relation between the joule and the calorie is given as
$1\,{\text{Calorie}} = 4.186\,{\text{Joules}}$
Hence the number of joules equivalent to one kilocalorie will be equal to
$1\,{\text{kiloCalorie}} = 4186\,{\text{Joules}}$

Hence the correct choice will be option (B).

Note: The experimental measurements of energy in the units of joule and calorie are done experimentally and as over the years, our measurement techniques improve, the relations between the two units have become more accurate. The joule and the calorie are the most widely used units of energy so we must be aware of their interconversions. The CGS unit of energy is ergs and not calories.