energy, entropy and equilibrium. these are some standard entropy values. notice that the units are j...

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Energy, entropy and equilibrium

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Page 1: Energy, entropy and equilibrium. These are some standard entropy values. Notice that the units are J K –1 mol –1. These are different from the units for

Energy, entropy and equilibrium

Page 2: Energy, entropy and equilibrium. These are some standard entropy values. Notice that the units are J K –1 mol –1. These are different from the units for

These are some standard entropy values. Notice that the units are J K–1 mol–1. These are different from the units for enthalpy, kJ mol–1.

Page 3: Energy, entropy and equilibrium. These are some standard entropy values. Notice that the units are J K –1 mol –1. These are different from the units for

Let's work out the standard entropy change, ΔSө, for the decomposition of calcium carbonate.

Page 4: Energy, entropy and equilibrium. These are some standard entropy values. Notice that the units are J K –1 mol –1. These are different from the units for

We need to know the total standard entropy of the products and the total standard entropy of the reactants.

Page 5: Energy, entropy and equilibrium. These are some standard entropy values. Notice that the units are J K –1 mol –1. These are different from the units for

First, add up all the entropy values for the products, in this case calcium oxide and carbon dioxide.

Page 6: Energy, entropy and equilibrium. These are some standard entropy values. Notice that the units are J K –1 mol –1. These are different from the units for

Next, subtract all the entropy values for the reactants. In this case there is only one, calcium carbonate.

Page 7: Energy, entropy and equilibrium. These are some standard entropy values. Notice that the units are J K –1 mol –1. These are different from the units for

The standard entropy change for the decomposition of calcium carbonate is positive.

Page 8: Energy, entropy and equilibrium. These are some standard entropy values. Notice that the units are J K –1 mol –1. These are different from the units for

These are some standard entropy values. Notice that the units are J K–1 mol–1. These are different from the units for enthalpy, kJ mol–1.

Page 9: Energy, entropy and equilibrium. These are some standard entropy values. Notice that the units are J K –1 mol –1. These are different from the units for

Let's work out the standard entropy change, ΔSө, for the synthesis of ammonia.

Page 10: Energy, entropy and equilibrium. These are some standard entropy values. Notice that the units are J K –1 mol –1. These are different from the units for

We need to know the total standard entropy of the products and the total standard entropy of the reactants.

Page 11: Energy, entropy and equilibrium. These are some standard entropy values. Notice that the units are J K –1 mol –1. These are different from the units for

First, add up all the entropy values for the products, in this case ammonia. Note that we multiply its entropy value by 2.

Page 12: Energy, entropy and equilibrium. These are some standard entropy values. Notice that the units are J K –1 mol –1. These are different from the units for

Next, subtract all the entropy values for the reactants, starting with nitrogen.

Page 13: Energy, entropy and equilibrium. These are some standard entropy values. Notice that the units are J K –1 mol –1. These are different from the units for

Note that we multiply the entropy value for hydrogen by 3.

Page 14: Energy, entropy and equilibrium. These are some standard entropy values. Notice that the units are J K –1 mol –1. These are different from the units for

Remember to multiply where necessary.

Page 15: Energy, entropy and equilibrium. These are some standard entropy values. Notice that the units are J K –1 mol –1. These are different from the units for

The standard entropy change for the synthesis of ammonia is positive.

Page 16: Energy, entropy and equilibrium. These are some standard entropy values. Notice that the units are J K –1 mol –1. These are different from the units for

We can work out the entropy change in the surroundings when a chemical change occurs.

Page 17: Energy, entropy and equilibrium. These are some standard entropy values. Notice that the units are J K –1 mol –1. These are different from the units for

To do this we need to know the enthalpy change and the temperature at which the reaction occurs.

Page 18: Energy, entropy and equilibrium. These are some standard entropy values. Notice that the units are J K –1 mol –1. These are different from the units for

If we know the entropy change for the reaction (the system) and the entropy change for the surroundings, we can work out the total entropy change.

Page 19: Energy, entropy and equilibrium. These are some standard entropy values. Notice that the units are J K –1 mol –1. These are different from the units for

First calculate the enthalpy change, ΔH, for the reaction.

Page 20: Energy, entropy and equilibrium. These are some standard entropy values. Notice that the units are J K –1 mol –1. These are different from the units for

The enthalpy change is 92.4 kJ mol–1. Remember to multiply by 1000 because entropy values are in J K–1 mol–1.

Page 21: Energy, entropy and equilibrium. These are some standard entropy values. Notice that the units are J K –1 mol –1. These are different from the units for

Divide by the temperature, in this example 298 K.

Page 22: Energy, entropy and equilibrium. These are some standard entropy values. Notice that the units are J K –1 mol –1. These are different from the units for

The entropy change in the surroundings in this example is –310 J K–1 mol–1.

Page 23: Energy, entropy and equilibrium. These are some standard entropy values. Notice that the units are J K –1 mol –1. These are different from the units for

Now let's calculate the total entropy change.

Page 24: Energy, entropy and equilibrium. These are some standard entropy values. Notice that the units are J K –1 mol –1. These are different from the units for

First, substitute the entropy change for the surroundings that we have just calculated.

Page 25: Energy, entropy and equilibrium. These are some standard entropy values. Notice that the units are J K –1 mol –1. These are different from the units for

Next, substitute the entropy change for the system. In this example it is +93 J K–1 mol–1.

Page 26: Energy, entropy and equilibrium. These are some standard entropy values. Notice that the units are J K –1 mol –1. These are different from the units for

The total entropy change here is negative. As it would lead to a decrease in entropy, the reaction would not happen spontaneously at 298 K.

Page 27: Energy, entropy and equilibrium. These are some standard entropy values. Notice that the units are J K –1 mol –1. These are different from the units for

The total entropy change must be positive for a reaction to happen. If it is zero, the reaction forms an equilibrium.

Page 28: Energy, entropy and equilibrium. These are some standard entropy values. Notice that the units are J K –1 mol –1. These are different from the units for

The total entropy change must be positive for a reaction to happen. If it is zero, the reaction forms an equilibrium.

Page 29: Energy, entropy and equilibrium. These are some standard entropy values. Notice that the units are J K –1 mol –1. These are different from the units for

We can work out the minimum temperature at which the total entropy change is zero.

Page 30: Energy, entropy and equilibrium. These are some standard entropy values. Notice that the units are J K –1 mol –1. These are different from the units for

We can work out the minimum temperature at which the total entropy change is zero.

Page 31: Energy, entropy and equilibrium. These are some standard entropy values. Notice that the units are J K –1 mol –1. These are different from the units for

This equation shows the relationship between the enthalpy change, the temperature and the entropy change of the system when the total entropy change is zero.

Page 32: Energy, entropy and equilibrium. These are some standard entropy values. Notice that the units are J K –1 mol –1. These are different from the units for

We can rearrange the equation to find the temperature at which the total entropy change is zero.

Page 33: Energy, entropy and equilibrium. These are some standard entropy values. Notice that the units are J K –1 mol –1. These are different from the units for

The enthalpy change when ice melts is 6.01 kJ mol–1, which is 6010 J mol–1. The corresponding change in the entropy of the system is 22 J K–1 mol–1.

Page 34: Energy, entropy and equilibrium. These are some standard entropy values. Notice that the units are J K –1 mol –1. These are different from the units for

The total entropy will be zero at 273 K or 0 °C. At this temperature, ice and liquid water exist together in equilibrium.