3.1a Some Comments about Units
A Reminder:
Remember that there are different ways to express fractions. You should be comfortable seeing units in any of the alternate forms. For example:
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J · K-1·mol-1 |
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Another important note about the units
| When we are concerned with S, the units are J · K-1·mol-1 or |
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| But with ΔS the units become just J·K-1 or |
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| Why the difference? S always refers to one mole of a specific substance - element or molecule. ΔS refers to a change in entropy for an entire system (all reactants and products). We are no longer talking about one mole of any specific, individual substance, but rather by how much the entire system has changed. This was true for ΔH as well - heat of formation, ΔH°f refers to one mole of a specific substance, whereas the heat of reaction, ΔH, refers to the change undergone by the entire system. | ||