topic 13b: entropy Flashcards
1
Q
why does enthalpy changed alone not determine whether reactions occur
A
endothermic reactions can still occur
2
Q
what is entropy
A
measure of disorder of a system
3
Q
order of priority when considering entropy
A
- state (gas>liquid>solid)
- increase in number of molecules
4
Q
explain entropy changes for states
A
- solid lowest entropy as particles can only vibrate about fixed positions. lowest disorder
- liquid more as can slide over each other, but confined by container. more disorder
- gases the most as free to move beyond confines of container. most diosrder
- boiling is a bigger increase in entropy than melting
5
Q
unit of entropy
A
J/K/Mol
6
Q
perfect crystal
A
- zero entropy
- at abosulte 0 (0K)
7
Q
delta s system
A
- entropy products - entropy reactants
8
Q
delta s surroundings
A
- delta h (j) / T
9
Q
total entropy change (delta s total)
A
delts s system + delta s surroundings
10
Q
if a reaction is spontaneous then … (delta s total)
A
is POSITIVE
11
Q
delta G
A
delta H - T delta s system
if negative then feasible
12
Q
delta g unit
A
j or kj / mol
13
Q
delta g during physical phase changes
A
0
eg melting boiling etc
14
Q
delta g in terms of equilibrium
A
delta g = -RT lnK
15
Q
EVEN IF A REACTION IS FEASIBLE, WHY MIGHT IT STILL NOT OCCUR
A
- activatoin energy barrier too high
