Question

If the heat of combustion for a specific compound is -1270.0 kJ/mol and its molar mass is 27.33 g/mol, how many grams of this compound must you burn to release 200.00 kJ of heat?

Answer 1

We are given heat of combustion. The given heat of combustion has negative sign this indicates that heat is given when the substance is combusted. Also it has unit in kJ /mol which mean the heat given when 1 mol of the substance is burnt or combusted. We use this value and find out the number of moles required to release 200.00 kJ of heat.

Once we get the moles then by using molar mass we can calculate mass of the substance.

Step 1

Calculation of mol

n substance = 200.00 kJ x 1 mol / 1270.0 kJ

                   =0.1575 mol substance.

                 

Step calculation of mass

Mass of the substance = mol substance x molar mass

            = 0.1575 mol substance x 27.33 g /mol

            =4.30 g

Ans : Mass of the substance needed to produce 200.00 kJ of heat is 4.30 g