When the spark ignites the mixture in an engine, what occurs?

When the spark ignites the mixture in an engine, a rapid chemical reaction occurs, leading to the combustion of the air-fuel mixture. This reaction generates a significant amount of heat, which causes a substantial increase in temperature within the combustion chamber. As the temperature rises, the pressure also increases due to the ideal gas law, which states that an increase in temperature at constant volume will result in an increase in pressure.

The rise in temperature and pressure is crucial for the performance of the engine, as it creates the force necessary to push the piston down during the power stroke. This phenomenon is integral to the functioning of an internal combustion engine, as it transforms the chemical energy of the fuel into mechanical energy.

The other choices address various aspects of combustion, but the direct and immediate result of ignition is indeed the increase in both temperature and pressure in the cylinder, leading to the expansion of gases that drives the piston down. This is a fundamental principle of how gas engines operate, emphasizing the relationship between temperature, pressure, and engine performance.