. One nutritional Calorie is equal to one kilocalorie (kcal). If a food package reports 165.0 Calories (Cal) per serving, how many calories (cal) are in each serving?

Answer 1

The key to solving this problem lies in the fact that nutritional Calories (Cal) are not the same as true thermodynamic calories (cal). The thermodynamic calorie (cal) unit is defined as containing a certain amount of energy to release when burned: specifically, the amount of energy required to raise the temperature of 1mL of water by 1 degree Celsius, or about 4.18 Joules.

Now, let’s consider the kilocalorie (kcal). Note the prefix “kilo” meaning 1,000. Also note that it refers to calorie with a small c (so, the thermodynamic definition rather than the nutritional definition). Putting that all together, we see that one kilocalorie (kcal) is the same as 1,000 thermodynamic calories (cal).

Ok. Now the problem tells us that 1 nutritional Calorie (Cal) is the same as one kilocalorie (kcal) which is true. So, if we have 165.0 Calories per serving, that is the same as 165.0 kcal per serving. As we saw above, 1 kcal is equal to 1,000 cal. So, 165.0 x 1,000 will give you your answer: 165,000.0 cal per serving.