Why does concentration affect rate of reaction

Differential rate laws are generally used to describe what is occurring on a molecular level during a reaction, whereas integrated rate laws are used for determining the reaction order and the value of the rate constant from experimental measurements. Below are three reactions and their experimentally determined differential rate laws. For each reaction, give the units of the rate constant, give the reaction order with respect to each reactant, give the overall reaction order, and predict what happens to the reaction rate when the concentration of the first species in each chemical equation is doubled.

Asked for: units of rate constant, reaction orders, and effect of doubling reactant concentration. B The exponent in the rate law is 2, so the reaction is second order in HI. Because HI is the only reactant and the only species that appears in the rate law, the reaction is also second order overall. The reaction rate will therefore quadruple. B The rate law tells us that the reaction rate is constant and independent of the N 2 O concentration.

That is, the reaction is zeroth order in N 2 O and zeroth order overall. C Because the reaction rate is independent of the N 2 O concentration, doubling the concentration will have no effect on the reaction rate.

B The only concentration in the rate law is that of cyclopropane, and its exponent is 1. This means that the reaction is first order in cyclopropane. Cyclopropane is the only species that appears in the rate law, so the reaction is also first order overall. C Doubling the initial cyclopropane concentration will increase the reaction rate from k [cyclopropane] 0 to 2 k [cyclopropane] 0. This doubles the reaction rate. Given the following two reactions and their experimentally determined differential rate laws: determine the units of the rate constant if time is in seconds, determine the reaction order with respect to each reactant, give the overall reaction order, and predict what will happen to the reaction rate when the concentration of the first species in each equation is doubled.

The number of fundamentally different mechanisms sets of steps in a reaction is actually rather small compared to the large number of chemical reactions that can occur. Thus understanding reaction mechanisms can simplify what might seem to be a confusing variety of chemical reactions. This can be done by designing experiments that measure the concentration s of one or more reactants or products as a function of time.

To do this, we might keep the initial concentration of B constant while varying the initial concentration of A and calculating the initial reaction rate. This information would permit us to deduce the reaction order with respect to A. Similarly, we could determine the reaction order with respect to B by studying the initial reaction rate when the initial concentration of A is kept constant while the initial concentration of B is varied.

In earlier examples, we determined the reaction order with respect to a given reactant by comparing the different rates obtained when only the concentration of the reactant in question was changed.

When concentrations are already high, a limit is often reached where increasing the concentration has little effect on the rate of reaction. When several reactants are involved, increasing the concentration of one of them may not affect the rate of reaction if not enough of the other reactants is available. Overall, concentration is only one factor influencing the rate of reaction, and the relationship is usually not simple or linear.

The rate of reaction in general varies directly with changes in the concentration of the reactants. When the concentration of all the reactants increases, more molecules or ions interact to form new compounds, and the rate of reaction increases. When the concentration of a reactant decreases, there are fewer of that molecule or ion present, and the rate of reaction decreases. In special cases such as for high concentrations, for catalytic reactions or for a single reactant, changing the concentration of reactants may not affect the rate of reaction.

In a typical chemical reaction, several substances react to form new products. The substances may be brought together as gases, liquids or in solution, and how much of each reactant is present affects how fast the reaction proceeds.

Often there is more than enough of one reactant, and the rate of the reaction depends on the other reactants present. Sometimes the rate of reaction can depend on the concentration of all the reactants, and sometimes catalysts are present and help determine the speed of the reaction. Don't assume that if you double the concentration of one of the reactants that you will double the rate of the reaction.

It may happen like that, but the relationship may well be more complicated. Note: The mathematical relationship between concentration and rate of reaction is dealt with on the page about orders of reaction.

If you are interested, you can use this link or read about it later via the rate of reaction menu link at the bottom of the page. The examples on this page all involve solutions. Changing the concentration of a gas is achieved by changing its pressure. This is covered on a separate page. Note: If you want to explore the effect of changing pressure on the rate of a reaction, you could use this link. Alternatively, use the link to the rates of reaction menu at the bottom of this page.

In the lab, zinc granules react fairly slowly with dilute hydrochloric acid, but much faster if the acid is concentrated. Solid manganese IV oxide is often used as a catalyst in this reaction. Oxygen is given off much faster if the hydrogen peroxide is concentrated than if it is dilute.

This is a reaction which is often used to explore the relationship between concentration and rate of reaction in introductory courses like GCSE. When a dilute acid is added to sodium thiosulphate solution, a pale yellow precipitate of sulphur is formed. As the sodium thiosulphate solution is diluted more and more, the precipitate takes longer and longer to form. The same argument applies whether the reaction involves collision between two different particles or two of the same particle.

In order for any reaction to happen, those particles must first collide. To gain an understanding of collision theory. To gain an understanding of the four main factors that affect reaction rate. Reactions occur when two reactant molecules effectively collide, each having minimum energy and correct orientation.