Find the Molar Mass of A: A + B + Energy = C | 35.5g A, 750kJ Heat Released

[Speedking96]

Homework Statement

2 A + 3 B + 1000 kJ ==> 4 C

where A,B,C are molecules. A mass of 35.5 g of A is used with the right quantity of B, and the mixture of reactants is heated with an energy of 750 kJ. Find the molar mass of A.

2. The attempt at a solution

Heat released per mole in terms of "A" : 1000 kJ / 2 = 500 kJ/mole "A"

Finding number of moles used:

(750 kJ) / (500 kJ/mole) = 1.5 mol "A"

Molar mass = (35.5 grams) / (1.5 mol) = 23.7 g/mol

 

[Borek]

Your approach looks OK, but the question is poorly worded - it doesn't say anything about whether there was enough heat to react all of A.