13b - entropy Flashcards
what is entropy?
measures the disorder in a system / number of ways energy could be arranged in a system
what are the problems with ^H that entropy has to be taken into account?
spontaneous exothermic reactions produce thermodynamically stable products
- how are some endothermic reactions also spontaneous?
by what factors are ^S system affected?
- changing of state
- increase in num. of molecules
at what conditions would entropy = 0?
perfect crystal lattice at 0 K
how is ^S system calculated?
S products - S reactants
how is ^S surroundings calculated?
-^H reaction / T
what would the sign of entropy be if reaction is spontaneous?
positive
explain the sign of ^S surroundings in an exothermic reaction.
+ive
- energy given out to surroundings
-> more ways of arranging molecules (in surroundings)
explain the sign of ^S surroundings in an endothermic reaction.
-ive
- energy transferred from surroundings
-> less ways of arranging energy from surroundings
what does the gibbs free energy change determine?
feasibility of reaction
what are the 2 equations for ^G?
^G = ^H - T^S system
^G = RTlnk
explain the sign of ^G when a reaction is feasible & spontaneous.
^G negative
- high entropy (positive ^S system ) & negative ^H (exothermic)
what is an exception to ^G not being spontaneous?
high activation energy
what would be the value of ^G when state change occur? explain why.
0
- physical phase changes are in equilibrium
how does temperature affect ^G with increasing & decreasing entropy?
increasing entropy:
- increasing temperature makes ^G more likely to be -ive (as ^S sys +ive) -> more likely reaction will occur
decreasing entropy:
- increasing temperature makes ^G more likely to be +ive (^S sys -ive) -> more likely reaction will not occur
