## Homework 9.45

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

aristotelis1H
Posts: 16
Joined: Fri Sep 25, 2015 3:00 am

### Homework 9.45

"9.45 Use the information in Table 8.3 to calculate the changes in entropy f the surroundings and of the system for (a) the vaporization of 1.00 mol CH4(l) at its normal boiling point; (b) the melting of 1.00 mol C2H5OH(s) at its normal melting point; (c) the freezing of 1.00 mol C2H5OH(l) at its normal freezing point"

When solving for part (c) and using

ΔSsys = $\frac{ΔHsystem}{T}$

Is the ΔHofus value negative because heat is released from a system when freezing an object?

Dahriel Aron 3A
Posts: 60
Joined: Fri Sep 25, 2015 3:00 am

### Re: Homework 9.45

for this problem, I was also wondering why they divide the enthalpy of fusion for ethanol by the freezing point and not the melting point to find its melting entropy

Jacob Afable 3J
Posts: 41
Joined: Fri Sep 25, 2015 3:00 am

### Re: Homework 9.45

aristotelis1H wrote:"9.45 Use the information in Table 8.3 to calculate the changes in entropy f the surroundings and of the system for (a) the vaporization of 1.00 mol CH4(l) at its normal boiling point; (b) the melting of 1.00 mol C2H5OH(s) at its normal melting point; (c) the freezing of 1.00 mol C2H5OH(l) at its normal freezing point"

When solving for part (c) and using

ΔSsys = $\frac{ΔHsystem}{T}$

Is the ΔHofus value negative because heat is released from a system when freezing an object?

ΔHofus indicates the amount of energy it takes to melt C2H5OH(l). So the value would be negative since the process is reversed (freezing). E.g. A -Hofus is used when changing water to ice.