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I know that having a negative delta g tells us that the reaction is spontaneous. When we are looking at delta s the total change in entropy being positive would also tell us the reaction would be spontaneous. Is this because a large delta s is being subtracted from delta h making delta g more negative?
If delta S is larger than delta H, it would make delta G negative (spontaneous). However, we would need to know the exact values for this. Another situation in which the reaction is spontaneous is if delta H is negative and delta S is positive. Subtracting a positive from a negative gives us a negative value for delta G, showing that the reaction is spontaneous. This situation doesn't require exact walls and is more general.
We can only tell if a reaction is spontaneous based on delta S alone is delta S total > 0. This is because spontaneous reactions follow the second law of thermodynamics, which is that entropy is always increasing. If delta S total is > 0, entropy is increasing and the reaction is spontaneous.
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