Question

Which of the following energy quantities is equivalent to 578 J?

Answer 1

Answer:

• 0.138 kcal

Explanation:

The answer choices are:

• a) 5.78 × 10⁵ kJ

• b) 138 kcal

• c)0.138 kcal

• d)1.38 × 10⁵ kcal

Solution

You must use the conversion factors to convert J to kcal.

• 1cal = 4.184J

        Dividing both sides by 4.184J:

        ⇒ 1 = 1cal/4.184J

• 1kcal = 1,000cal

       Dividing both sides by 1,000 cal

        ⇒ 1 = 1kcal / 1,000 cal

Mutiply 578J by the conversion factors to find kcal:

       $578J\times 1cal/4.184J\times 1kcal/1,000cal=0.138kcal$

Notice how the units J and cal cancel to yield kcal at the end.