Calculate the number of kilojoules to warm 125 g of iron from 23.5 °c to 78.0 °c.

Given: 
Iron, 125 grams T
1 = 23.5 degrees Celsius, T2 = 78 degrees Celsius.   

Required: 
Heat produced in kilojoules   

Solution: 
The molar mass of iron is 55.8 grams per mole. SO we need to change the given mass of iron into moles.   
 
Number of moles of iron = 125 g/(55.8 g/mol) = 2.24 moles   

Q (heat) = nRT = nR(T2 = T1) 
Q (heat) = 2.24 moles (8.314 Joules per mol degrees Celsius) (78.0 degrees Celsius – 23.5 degrees Celsius) 
Q (heat) = 1014.97 Joules or 1.015 kilojoules This is the amount of heat produced in warming 125 g f iron.