How can calories be converted to kilocalories?Our book states that: 1 cal = 4.186 J and 1 kcal = 4186 J. Is this correct?
This question is basically about the meaning of the prefix "kilo." Kilo is used to represent a quantity that is 1000 or 10^3 times the basic unit. Here the basic unit is calorie. Kilocalorie is equal to 1000 calories, just like kilometer is equal to represent 1000 meters.
To convert calories to kilocalories you have to divide the number of calories by 1000.
X calories = X/1000 kilocalories.
Your book has it right that 1 cal = 4.186 J and 1 kcal = 4186 J.
As you will notice 4186 = 4.186*1000, just as 1 kcal = 1000 cal.
The rule for conversion is 1 cal = 1/1000 kcal and 1 kcal = 1000 cal.
A calorie is a unit of energy, or heat, needed to raise the temperature of 1 gram of water by 1 degree centigrade. "Kilo" means 1000 and therefore, a kilocalorie is 1000 calories. A kilocalorie also is known as a dietary calorie, or the amount of heat needed to raise the temperature of 1 kg of water by 1 degree centigrade.
If you are interested in the conversion only, divide the number of calories by 1000. For example, 500 calories = 0.5 kilocalories.