word problem

Question

500. g of water were heated from 20 to 50 celsius. How many kilocalories were neeeded to bring about this temperature change?  

Answer 1

First of all, since they are asking about kilocalories, you have to work with kilograms, not grams.  So change the mass units of the water from g to kg:  500 g = 0.5 kg

 

The temperature of .5 kg of water changed by 30 °C.  Since the specific heat of water is 1, that means that 0.5 * 30 = 15 kcal of heat was needed.