Calorimeters in Chemistry

Question

Calorimeters can be used to determine how much energy is in food. The energy in food is usually expressed in calories or kilocalories. A calorie is the amount of energy needed to change the temperature of 1g of water by 1 degrees Celsius. There are 1000 calories in a kilocalorie.

a. How many Joules are in 1 calorie?

b. Suppose a snack bar is burned in a calorimeter and heats 2000g of water by 20.0 degrees Celsius. How much heat energy was released? Give your answer in both Joules and calories.

c. How many kilocalories does the snack bar contain?

Answer 1

A. one calorie is equal to 4.184 joules.

B. The specific heat of water is 1 calorie per gram-°C. The heat required to raise the temperature of 2000 g water by 20°C is 1.00 cal/g-C x 2000 g x 20 °C = 40000 calories or 167360 joules.

C. There are 1000 cal/kcal. #kcal = 1 kcal/1000 cal x 40000 cal = 40 kcal.