Question

hydrogen gas is burned in the presence of oxygen, in a cylinder that has a freely moving piston. the piston moves as a result of work being performed on it (and the surrounding atmosphere) and eventually the piston and the gas products cool to room temperature with the release of heat energy.
what is the sign of the overall q, and is the process exothermic or endothermic?
q is positive and the overall process is exothermic
q is positive and the overall process is endothermic
q is negative and the overall process is exothermic
q is negative and the overall process is endothermic
dont test me yet, i am trying to gain an understanding before attempting to answer this question.

Explanation:

• Combustion of hydrogen gas (\(2H_2 + O_2

ightarrow2H_2O\)) is an exothermic reaction. In thermodynamics, for an exothermic process, heat is released to the surroundings.

• The sign convention: \(q>0\) (positive) when heat is absorbed by the system and \(q < 0\) (negative) when heat is released by the system. Since the hydrogen - oxygen combustion (a chemical reaction which is part of the system) releases heat (exothermic), \(q\) (heat change of the system) is negative.
• An exothermic process is one where the system releases heat. So the overall process (hydrogen combustion) is exothermic.

Answer:

q is negative and the overall process is exothermic.