- #1

Titan97

Gold Member

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## Main Question or Discussion Point

I have some doubts on entropy change of certain simple process. Can you check if these statements are correct? This is what I know:

Since the system does not alter the surroundings, ##\Delta S_{Surr}=0##.

How can I compute ##\Delta S_{Surr}##?.

$$H=U+pV$$

$$dU=dQ-pdV$$

$$dH-d(pV)=dQ-pdV$$

$$dH=dQ+VdP=dQ$$

since P is constant.

Hence, $$dS_{sys}=\frac{dH}{T}$$

How can I compute ##\Delta S_{Surr}##?.

For example, if an ice melts, ice is the 'system' and the medium where its kept is the 'surroundings'

The statements in red are questions. Those in blue means 'I am not sure if its correct'. (I might have written meaningless/incorrect/stupid statements. I just want to be clear with entropy before writing my exam.)

**For a reversible adiabatic process**, $$\Delta Q=0$$. $$\Delta S_{system}=\frac{\Delta Q}{T}=0$$.

Since the system does not alter the surroundings, ##\Delta S_{Surr}=0##.

**For a reversible isothermal process**, $$\Delta S_{system}=nR\ln{\frac{V_2}{V_1}}$$

How can I compute ##\Delta S_{Surr}##?.

**For any phase change**, since temperature and pressure is constant,

$$H=U+pV$$

$$dU=dQ-pdV$$

$$dH-d(pV)=dQ-pdV$$

$$dH=dQ+VdP=dQ$$

since P is constant.

Hence, $$dS_{sys}=\frac{dH}{T}$$

How can I compute ##\Delta S_{Surr}##?.

For example, if an ice melts, ice is the 'system' and the medium where its kept is the 'surroundings'

The statements in red are questions. Those in blue means 'I am not sure if its correct'. (I might have written meaningless/incorrect/stupid statements. I just want to be clear with entropy before writing my exam.)