## Entropy based on initial temp

$\Delta S = \frac{q_{rev}}{T}$

Anika_Patel_1G
Posts: 32
Joined: Fri Sep 29, 2017 7:06 am

### Entropy based on initial temp

At the end of lecture on Friday, Dr. Lavelle mentioned that if two gases (one at a lower temperature than the other) had the same amount of energy added to them, the change in entropy would be much greater for the gas that started at a lower temperature. Why is this? Why does the magnitude of deltaS depend on the temperature at which heat is transferred?

Masih Tazhibi 2I
Posts: 33
Joined: Fri Sep 29, 2017 7:06 am

### Re: Entropy based on initial temp

Changes in entropy are based on the equation q/T.

It intuitively makes sense that if you held q constant in both cases, lets say 100J, the change in entropy would be less with a higher temperature.

For example, 100J/200K is greater than 100J/500k. This is logical because adding a constant amount of heat would have less impact at higher temperatures. 100J of added heat would have a much higher impact on the thermal entropy of ice than it would on that of hot water, because the heat put into the system would be very high compared to the heat already in the system.

Dylan Davisson 2B
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### Re: Entropy based on initial temp

It is expected for the change of entropy to be greater when the temperature is low rather than high, because the energy that is brought into the system stirs up the molecules of the colder system much more than that of the warmer system. The molecules of the lower temperature gas initially has little thermal motion because it is colder, whereas the molecules of the higher temperature gas has noticeable initial thermal motion. The effect of the energy on the colder gas is much more noticeable because the molecules of with little thermal motion suddenly begin to move with great thermal motion. This effect is not as great with the hotter gas because the molecules are already moving substantially. So, the entropy of the lower temperature gas sees greater change when energy is applied.

Jessica Jones 2B
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### Re: Entropy based on initial temp

When finding the deltaS for a freezing reaction, would you use -deltaHfusion instead of +deltaHfusion?