Question

Complete combustion of 1.0 metric ton of coal (assuming pure carbon) to gaseous carbon dioxide releases 3.3 x 1010 j of heat. convert this energy to kilocalories

Answer 1

Keeping in mind that the conversion between calories and Joules is
$1 cal = 4.186 J$
we can write the conversion factor using the kilocalories:
$1 kcal = 4186 J$

The energy released in our problem is
$E=3.3 \cdot 10^{10} J$ 
so we can set a simple proportion to find its equivalent in kcal:
$1 kcal: 4186 J = x: 3.3 \cdot 10^{10} J$
from which we find:
$x= \frac{3.3 \cdot 10^{10} J \cdot 1 kcal}{4186 J} =7.88 \cdot 10^6 kcal$