Question

According to the heats of reaction at 101.3 kPa and 298 K, which equation represents a change resulting in the greatest quantity of energy released?

a) H2(g) + O2(g) → H2O(g)
b) CO(g) + 2H2(g) → CH3OH(g)
c) C(s) + O2(g) → CO2(g)
d) N2(g) + 3H2(g) → 2NH3(g

Answer 1

The reaction representing the greatest quantity of energy released is the combustion of carbon to form CO2, with -393.5 kJ of energy per mole of CO2 released, indicating an exothermic reaction.

Step-by-step explanation:

The question deals with comparing the quantity of energy released in various chemical reactions given their heats of reaction at a certain condition (101.3 kPa and 298 K). An exothermic reaction releases energy, while an endothermic reaction absorbs energy. The negative sign indicates an exothermic reaction, while a positive sign indicates an endothermic reaction.

For the reactions provided:

• Reaction a, the combustion of hydrogen gas to form water, is highly exothermic, releasing 286 kJ per mole of water formed when in a gaseous state. If liquid water forms, it's even higher at 286 kJ.
• Reaction b, the formation of methanol from CO and H2, is not provided but we could assume it is exothermic because it forms a more complex molecule from simpler ones.
• Reaction c, the formation of carbon dioxide from carbon and oxygen, is also exothermic, releasing -393.5 kJ per mole of CO2 formed.
• Reaction d, the synthesis of ammonia from nitrogen and hydrogen, is also an exothermic process with a significant heat release associated with it. However, the exact heat release is not provided in the information given.

Based on the available data, Reaction c associated with the combustion of carbon to form CO2 is the one that represents the greatest quantity of energy released since it results in -393.5 kJ per mole of CO2, which is a larger energy release than for the formation of water from hydrogen and oxygen.