# Unit 5 section 1 entropy

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## What is entropy?

How much disorder is in a system.

It is a measure of the number of ways that particles can be arranged and the number of ways that the energy can be shared between particles.

Represented by symbol S

Physical state affects entropy, from solid-liquid-gas entropy increases. ordered, some disorder and chaotic.

Dissolution increases enthalpy because the dissolved particles can move freely as they are no longer held in place.

Number of particles affects entropy. More particles means more entropy because there are more ways they and their energy can be arranged.

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## Spontaneous endothermic reactions

The entropy increases so much that the reaction will happen by itself, without you supplying energy.

Evaporation of water:
Needs energy to break the intermolecular bonds so it's endothermic but because it changes state the entropy increases.

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## Effects of entropy change

Spontaneous reactions won't happen unless the total entropy change in positive(/S+).

There is an entropy change between the reactants and products - the entropy change of the system.

The entropy of the surroundings changes aswell because energy is transferred to or from the system.

Total entropy change is the sum of the entropy changes of the system and the surroundings.

S total = S system + S surroundings in joul per kelvin per mole jkmol.

S system = S products - S reactants

S surroundings = - /H in joule per mole divided by T in kelvin.

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