A 0.1946 g piece of magnesium metal is burned in a constant-volume calorimeter that has a heat capacity for the bomb only of 1349 J/°C. The calorimeter contains 5.00 x 102g of water and the temperature rise is 1.40°C. Calculate the heat of combustion of magnesium metal in kJ/g, given that thespecific heat of water is 4.184 J/g·°C.

The heat of combustion of magnesium metal is 24.76 kJ/gram

Explanation:

Step 1: Data given

Mass of magnesium sample = 0.1946 grams

Molar mass of magnesium = 24.3 g/mol

bomb calorimeter that has a heat capacity of 1349 J/°C

Mass of water = 500 grams

Temperature change = 1.40 °C

Step 2: Calculated heat released

Q = (1349 J/°C * 1.40 °C) + (500 grams * 4.184 J/g°C * 1.40 °C)

Q = 4817.4 J = 4.82 kJ

Step 3: Calculate the heat given off by the burning Mg, in kJ/g

4817.4 J / 0.1946 grams = 24755.4 J / gram = 24.76 kJ / gram

The heat of combustion of magnesium metal is 24.76 kJ/gram