To vaporize 2.00g of ammonia, 656 calories are required. How many kilojoules are required to vaporize the same mass of ammonia?

In order to know the answer to this question, you just simply convert calorie to kilojoule.

However, I'm not sure which calorie you're talking about. If you're referring to 'gram calorie' then it takes 2.74 kilojoules to vaporize the same mass of ammonia.

If it's kilocalories, then you need 2744.7 kilojoules to vaporize it.