Here is a paragraph in Barron's SAT chemistry prep book:

Work itself is measured in Joules, and so is energy. In some problems, however, energy may be expressed in kilocalories. The relationship between these two units is that $4.18\times10^8$ Joules equals 1 kilocalorie (kcal).

Is this correct? Isn't 1 kilocalorie 4180 Joules?

  • $\begingroup$ Also note that names of units such as ‘joule’ are spelled with a lower case initial in English. (For SI units, it is only the unit name ‘degree Celsius’ that contains a capital letter.) $\endgroup$ – user7951 May 19 '19 at 6:35
  • 3
    $\begingroup$ It's likely just 3 being mistaken for 8 by typesetter as they are similar in some fonts and handwritings. $\endgroup$ – Džuris May 19 '19 at 9:06

This should never have happened in the scientific community, but:

The energy values of food are measured by the Calorie, with a capital C. A Calorie is equal to 1,000 calories or 1 kilocalorie (kcal).

Source: here

It is possible that Barron's got confused between Calorie and calorie. Even so, they still would be off by a factor of 100.

According to Wikipedia:

The SI unit of energy is the joule, with symbol "J"; one small calorie is now defined as exactly 4.184 J, and one large calorie is 4184 J. However, the two units are still used occasionally in technical work, and the large calorie is still widely used in nutrition.

So you are correct in saying that 1 "small" kilocalorie is 4180 joules. 1 "large" kilocalorie is $\pu{4.18e6 J}$, and maybe Barron's is now suggesting an "extra large" calorie.

More likely it is just a typo.


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