When methanol, CH3OH, is burned in the presence of oxygen gas, O2, a large amount of heat energy is released, as shown in the combustion reaction below.

Question

Based on the balanced thermochemical reaction above, how much heat is produced when 23.9 g of methanol react with 37.1 g of oxygen?

 

 

Equation Given:

 

CH3OH(g) + 3/2O2(g) --> CO2(g) + 2H2O(l)

Answer 1

To answer this problem you need to know the heat of reaction.  Methanol is a liquid at room temperature, and the heat of reaction for its combustion is -1452 kJ.

To solve the problem, first determine which reactant is limiting by converting each mass into moles:

23.9 g CH₃OH / 32.0419 g/mol = .746 mol

37.1 g O₂ / 31.9988 g/mol = 1.159 mol

Actual mol CH₃OH / mol O₂ = .746/1.159 = 0.644

Theoretical mol CH₃OH / mol O₂ = 0.67

The methanol is limiting (but not by much).

kJ = .746 mol CH₃OH (1452 kJ/ 2 mol CH₃OH) = 541.6 kJ