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Reversible vs. Irreversible processes

Posted: Fri Feb 08, 2019 2:19 am
by Janice Park 1E
Can someone explain why for reversible processes, as volume increases, pressure decreases, and temperature remains constant, but for irreversible processes, temperature changes along the pathway, and pressure remains constant as volume changes?

Re: Reversible vs. Irreversible processes

Posted: Fri Feb 08, 2019 8:59 am
by Ray Huang 1G
In a reversible reaction, we assume that the process occurs in minute increments back in forth but tending to one side. An increase in volume can be thought of as the volume increasing a little bit and then decreasing a bit and then increasing a bit. This allows for temperature to "balance out". Essentially, the temperature increases a little bit but then dissipates due to the amount of back and forth going on. Pressure decreases bc you expanded the gas and the number of moles haven't changed. In an irreversible reaction, all of this is happening more quickly. The temperature has no time to "even out" and pressure increases since it cannot balance out with the increase in volume. Think of it more like quickly allowing all of the air out of a scuba tank vs just letting some out at very small time intervals. The quick release is going to generate more pressure and heat.