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17.1 Factors that Influence Reaction Rates
When a chemical reaction takes place in a container which prevents the entry or escape of any of substances involved in the reaction, the quantities of these components change as some are consumed and others are formed. Eventually this change will come to an end, and the composition will remain unchanged as long as the system remains undisturbed. The system is then said to be in its equilibrium state, or more simply, "at equilibrium". A system at equilibrium has both reactants and product concentrations that stop changing because the forward and reverse rates have become equal. The system at equilibrium remains dynamic as both forward and reverse reactions are going. We observe no net change, however, as the reactions in both directions are balanced by changes in the other.
The ratio of constants in equilibrium reactions gives a new term, the equilibrium constant K. The equilibrium constant is a number equal to a particular ratio of equilibrium concentrations of product and reactant at a particular temperature. The magnitude of K is an indication of how far a reaction proceeds toward a product at a certain temperature.
- Small K: If a reaction yields very little product before reaching equilibrium.
- Intermediate K: When significant amounts of both reactant and product are present at equilibrium.
- Large K: If a reaction reaches equilibrium with very little reactant left.
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