# What is a kg.cal per gram, as a heat of combustion?

I see heats of combustion given in kg [dot] calories per gram molecular weight (Handbook of Chemistry and Physics, 1969-1970). I don't know how that makes sense, as I don't know what a kg cal might be. I would have expected units of energy per mass (calories per gram) or energy per mole. What is a kg cal, and what is wrong in my thinking?

• "gram" in the title of this thread should be "gram molecular weight". I previously misread the units in the table in the Handbook. Jun 22, 2015 at 22:15

$\mathrm{kg~cal}$ probably represents the kilogram calorie (especially given that it is an old book). Nowadays it is usually just known as the Calorie, usually abbreviated $\mathrm{kcal}$. It is roughly the amount of energy required to raise the temperature of $1~\mathrm{kg}$ of water by $1~\mathrm{^\circ C}$. Since this is temperature and pressure dependent, there are slight variations in the actual definition depending on the context in which it is used.
• The kilogram calorie is a unit of energy, not energy times mass, despite the name. It is named 'kilogram' to distinguish it from the 'normal' calorie which is the energy required to heat $1~\mathrm{g}$ of water by $1~^\circ C$. However, the kilogram calorie ($\mathrm{kcal}$) has become the 'normal' calorie due to its extensive usage in food labelling and is now colloquially referred to just as the calorie.