Factors Affecting Rate Of Reaction


Factors Affecting Rate Of Reaction

帖子 由 lonelytree 于 周一 五月 24, 2010 5:37 am

It's useful to be able to predict whether an action will affect the rate
at which a chemical reaction proceeds. There are several factors that
can influence the rate of a chemical reaction. In general, a factor that
increases the number of collisions between particles will increase the
reaction rate and a factor that decreases the number of collisions
between particles will decrease the chemical reaction rate.
Concentration of Reactants(Rate Constant Not Affected)
A higher concentration of reactants leads to more effective collisions
per unit time, which leads to an increasing reaction rate (except for
zero order reactions). Similarly, a higher concentation of products
tends to be associated with a lower reaction rate. Use the partial
pressure of reactants in a gaseous state as a measure of their
Temperature (Rate Constant Affected)
Usually, an increase in temperature is accompanied by an increase in the
reaction rate. Temperature is a measure of the kinetic energy of a
system, so higher temperature implies higher average kinetic energy of
molecules and more collisions per unit time. A general rule of thumb for
most (not all) chemical reactions is that the rate at which the
reaction proceeds will approximately double for each 10°C increase in
temperature. Once the temperature reaches a certain point, some of the
chemical species may be altered (e.g., denaturing of proteins) and the
chemical reaction will slow or stop.
Medium (Rate Constant Not Affected)
The rate of a chemical reaction depends on the medium in which the
reaction occurs. It may make a difference whether a medium is aqueous or
organic; polar or nonpolar; or liquid, solid, or gaseous.
Presence of Catalysts and Competitors (Rate Constant Affected)

(e.g., enzymes) lower the activation energy of a chemical reaction and
increase the rate of a chemical reaction without being consumed in the
process. Catalysts work by increasing the frequency of collisions
between reactants, altering the orientation of reactants so that more
collisions are effective, reducing intramolecular bonding within
reactant molecules, or donating electron density to the reactants. The
presence of a catalyst helps a reaction to proceed more quickly to
equilibrium. Aside from catalysts, other chemical species can affect a
reaction. The quantity of hydrogen ions (the pH of aqueous solutions)
can alter a reaction rate. Other chemical species may compete for a
reactant or alter orientation, bonding, electron density, etc., thereby
decreasing the rate of a reaction.

Click here for extra help on rate of reaction and reaction kinetics.

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