Question

molecular hydrogen, h₂ may be an excellent alternative to the hydrocarbon fuels from petroleum products, since the only product of combustion is water. combustion of hydrogen is obviously exothermic, heat energy is released after the combustion is complete and the engine has cooled down. which best describes the value for q and δh for the overall hydrogen combustion process?
2 h₂(g) + o₂(g) → 2 h₂o (l)
hydrogen oxygen water
q is positive and δh is positive.
q is positive and δh is negative.
q is negative and δh is positive.
q is negative and δh is negative.
dont test me yet, i am trying to gain an understanding before attempting to answer this question.

Explanation:

Step1: Define heat and enthalpy change

In thermochemistry, \( q \) (heat) is negative for exothermic reactions (heat released). \( \Delta H \) (enthalpy change) is also negative for exothermic reactions as \( \Delta H=H_{products}-H_{reactants} \), and energy is released (products have lower energy).

Step2: Analyze hydrogen combustion

Hydrogen combustion is exothermic (heat released). So \( q<0 \) (negative) as heat is lost by the system (reaction mixture). \( \Delta H <0 \) (negative) because it's an exothermic reaction.

Answer:

q is negative and \( \Delta H \) is negative.