In the presence of excess oxygen, methane gas burns in a constant-pressure system to yield carbon dioxide and water: CH₄ (g) + 2O₂ (g) → CO₂ (g) + 2H₂O (l) △H = -890.0 kJ
Calculate the value of q (kJ) in this exothermic reaction when 1.70 g of methane is combusted at constant pressure.

Question

Quizplus · Accepted Answer

First, we need to convert the mass of methane given in the problem to moles:

1.70 g CH4 x (1 mol CH4 / 16.05 g CH4) = 0.106 mol CH4

Now we can use the balanced chemical equation to determine the amount of energy released in the combustion of 0.106 mol CH4:

0.106 mol CH4 x (-890.0 kJ / 1 mol CH4) = -94.6 kJ

The negative sign indicates that the reaction is exothermic, and we use the value of -94.6 kJ because the problem asks for the value of q (the heat released) in kJ. Therefore, the best choice is A, -94.6.

In the Presence of Excess Oxygen, Methane Gas Burns in a Constant-Pressure