Question

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

Answer 1

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.