Question

Consider the following reaction:

2CH3OH(g)→2CH4(g)+O2(g),ΔH=+252.8 kJ

1. Calculate the amount of heat transferred when 28.0 g of CH3OH(g) is decomposed by this reaction at constant pressure.

2. For a given sample of CH3OH , the enthalpy change during the reaction is 82.3 kJ . What mass of methane gas is produced?

3. How many kilojoules of heat are released when 38.1 g of CH4(g) reacts completely with O2(g) to form CH3OH(g) at constant pressure?

Answer 1

1. Molar mass CH3OH is 32. 2 mols is 64. So you get 252.8 kJ when 64 g CH3OH is consumed. How much when only 28.0 g is consumed? That's
252.8 kJ x (28.0 g/64 g) = ? (note: g cancels with g and ? unit is kJ.

2. Same process. So you get 252.8 kJ when 2*16 = 32 g CH4 is produced. How many g CH4 when 82.3 kJ heat is produced? That's
32 g CH4 x (82.3 kJ/252.8 kJ) = ?

3. You should get the idea by now. Post your work if you want me to check it for #3. Good luck.