State and explain the factors that increase the entropy in a system
Entropy (symbol is S) is a measure of the randomness or disorder in a system. This tends to increase over time in a closed system. Gases mixing together increase the entropy.
The disorder of a system is highest when the particles are in the gaseous state and lowest when they are in the solid state. If the entropy increases, it produces a positive ΔS value.
Dissolution
Entropy increases when a solid is dissolved in a liquid. The ions in a lattice break apart and spread throughout the solution in a random arrangement. In addition, there is often an increase in the number of particles on the right hand side of the equation, such as:
Change of State
The entropy of a substance changes according to:
Hence, the entropy will increase when a solid goes into the liquid state, or when a liquid goes into the gaseous state. Sublimation also increases the entropy. Examples include:
Decomposition
This leads to an increase in the number of particles in the system, which causes an increase in entropy. For example:
Increase in Temperature
At higher temperatures, the kinetic energy of the particles increases, even if there is no change in state.
Predict whether the entropy change for a given reaction or process is positive or negative
There are some key indicators you can look for to tell whether the entropy is increasing or decreasing:
- State of the particles – are they going from solid to liquid/liquid to gas?
- The number of moles of particles on either side of the equation – if there is a greater number of moles on the right hand side, then the entropy
Calculate the standard entropy change for a reaction using the standard entropy values
The standard entropy change of reaction has the symbol ΔSӨ and units J K-1 or J K-1 mol-1. It is always measured at 1.01 x 102 kPa and 298 K. The standard entropy value for an element is always positive.
The change in entropy is calculated according to the equation:
Remember to multiply the S values by the number of moles of each substance in the reaction.
For example:
