18.6: Factors Affecting Reaction Rate
Sep 16, · Reactions occur when two reactant molecules effectively collide, each having minimum energy and correct orientation. Reactant concentration, the physical state of the reactants, and surface area, temperature, and the presence of a catalyst Author: Jessie A. Key. Sep 26, · The temperatures of the system, presence of a catalyst, exposure to radiation also affect the rate of reaction. Some of the important factors that affect the rate of reaction are: Effect of Concentration of Reactants on Rate of Reaction The rate of the reaction decreases with time.
Driving on a crowded freeway can get exciting. A lot of cars in a particular amount of space equals a high car concentration and many opportunities for unwanted connections with other cars. By their nature, some reactions what sort of glasses suit me very quickly, while others are very slow. However, certain changes in the reacting conditions can have an effect on the rate of a given chemical reaction.
Collision theory can be utilized to explain these rate effects. An increase in the concentration of one or more reacting substances results in an increase in the rate of reaction. When more particles are present in a given amount of space, a greater number of collisions will naturally occur between those particles. Since the rate of a reaction is dependent on the number of collisions occurring between reactants, the rate increases as the concentration increases.
When the pressure of a gas is increased its particles are forced closer together, decreasing in the process the amount of empty space between the particles.
Therefore, an increase in the pressure of a gas is also an increase in the concentration of the gas. For gaseous reactions, an increase in pressure increases the rate of reaction for the same reasons as described for an increase in concentration. Higher gas pressure leads to a greater number of collisions between reacting particles.
A large log placed in a fire will burn relatively slowly. If the same mass of wood were added to the fire in the form of small twigs, they would burn much more quickly. This is because the twigs provide a greater surface area than the log does. An increase in the surface area of a reactant increases the rate of a reaction. Surface area is larger when a given amount of a solid is present as smaller particles.
A powdered reactant has a greater surface area than the same reactant as a solid chunk. In order to increase the surface area of a substance, it may be ground into smaller particles or dissolved into a liquid. In solution, the dissolved particles are separated from each other and will react more quickly with other reactants. Raising the temperature of a chemical reaction usually results in a higher rate of reaction. When the reactant particles are heated, they move faster and faster.
This results in a greater frequency of collisions. A more important effect of the temperature increase is that the collisions occur with a greater force and are thus more likely to surmount the activation energy barrier and go on to form products.
Increasing the temperature of a reaction increases the number of effective collisions between reacting particles, so the reaction rate increases. Watch the video at the link below and answer the following questions:.
Skip to main content. Search for:. What are the chances of a fender-bender on the highway? Summary Factors affecting reaction rate are: concentration of reactants pressure if gas surface area temperature.
What was shown with the aluminum powder? What factor was mentioned, but not demonstrated? Review How does an increase in concentration of reactant increase rate? Why would rates increase with a larger surface area of reactants? What effect does temperature have on reaction rate? Licenses and Attributions. CC licensed content, Shared previously.
Feb 07, · The physical state of reactants, number of reactants, complexity of reaction and other factors highly influence the reaction rate as well. The rate of reaction is generally slower in liquids when compared to gases and slower in solids when compared to liquids. Size . An increase in the concentration of one or more reacting substances results in an increase in the rate of reaction. When more particles are present in a given amount of space, a greater number of collisions will naturally occur between those particles. Factors affecting reaction rate For a reaction to occur, the particles that are reacting must collide with each other. Only some of all the collisions that take place cause a chemical change to.
Copyright c Learning Top Notch. Learning Top Notch. The rate of a reaction between two substances depends upon the rate of collisions or rate of encounter between their molecules. The rate of encounter between reactant molecules is governed by many factors. Concentration, surface area, physical states, chemical nature of reactants and size of particles are some factors to name a few.
The temperatures of the system, presence of a catalyst, exposure to radiation also affect the rate of reaction. Some of the important factors that affect the rate of reaction are:. Effect of Concentration of Reactants on Rate of Reaction The rate of the reaction decreases with time. As the reaction proceeds, the concentration of reactants decrease while those of the products increase.
The change in the concentration of the various species takes place rapidly in the beginning. The rate of change of concentrations slows down with the advancement of time and as the reaction approaches the stage of completion the rate becomes very small. Thus, the inference which can be drawn is that the reaction depends on the concentration of the reactants. Higher the concentration of reactants, greater is the rate of reaction. Hence the rate of a reaction can be increased by increasing the concentration of one or more reactants and vice versa.
For the reactions taking place in the gaseous phase, the rate of reaction can be increased by increasing the partial pressure of the reacting gases.
When the partial pressure of the reacting gas or the concentration of a reactant is increased, the number of molecules per unit volume increases. This increases the rate if collisions between the reactant molecules resulting in an increase in the rate of the reaction. Effect of Physical State of Reactants on Rate of Reaction A reaction takes place only when there is an encounter between the molecules of the reactants.
During the encounter, the molecules of the reactants collide with one another and undergo chemical changes. The encounter between the molecules is possible only when they are free to move closer and intermix. In solid state, the constituent particles are held together by strong inter-particular forces and are unable to intermix freely. Therefore in the solid state, the reactants can interact only at their surfaces. Consequently, the collisions are not very effective.
However, in the liquid state as well as in the gaseous state, the molecules are free to move and the chances of their mutual collisions are much larger. Therefore, the reactions take place are much higher rates in the liquid and gaseous phases. When the reaction is allowed to proceed in a homogeneous manner the reaction mixture is homogeneous , the probability of encounter between reactant molecules is maximum.
Consequently, reactants react faster and the rate of the reaction is quire high. When the reactants are in the solid phase, it is very difficult to obtain a homogeneous mixture. However, when the reactants are in gaseous phase or when the reactants are in liquid phase, the reaction can easily be carried out in a homogeneous manner. Hence it may be concluded that a reaction will proceed faster if the reactants are mixed in the liquid phase or in the gaseous phase.
Effect of Surface Area and Particle Size of Reactants on Rate of Reaction The reactions in which reactants are present in different physical states are called heterogeneous reactions.
In case of such a reaction, the surface area and the size of the particles play and important role in deciding the rate of the reaction. This becomes more significant when one of the reacting species is a solid. The rate of a reaction involving a solid reactant increases with the increase in the surface area of the substance.
As the surface area increases, the area of contact between two reactants also increases. This enhances the rate of encounters between the molecules and consequently the rate of the reaction also increases. The surface area of a solid substance can be increased considerably by subdivision that is by dividing the larger particles into smaller particles.
This can be easily understood with the help of the following example. Diagram showing how surface area of a solid increases on subdivision. How surface area of a solid increases on subdivision. Thus on dividing the given cube into 27 smaller cubes the total volume remains the same but the surface area increases 3 times.
Thus, it may be concluded that the surface area of a solid reactant can be increased considerably by subdividing it into smaller particles.
Smaller the size of the particles, greater is the surface area and consequently greater is the rate of the reaction. Hence, in a heterogeneous system such as solid-liquid or solid-gas system, the fineness of solid particles deters the rate of the reaction. Finer the particles are, greater is the area of contact and consequently greater are the chances for the mutual collisions or encounters of the reactant molecules resulting in a greater reaction rate.
This is why coal dust burns in air faster as compared to a piece of coal. Similarly powdered sugar dissolves in water more rapidly as compared to sugar crystals. Effect of Temperature on Rate of Reaction Temperature has a significant effect on the rate of reactions. The rate of a chemical reaction increases with rise in temperature.
In most of the homogeneous reaction, the rate becomes doubled to trebled for each 10 rise in temperature. Thus, there is a tremendous effect of temperature on the reaction rate. The increase in the rate of reaction with rise in temperature is usually expressed in terms of quantity known as temperature coefficient. Temperature coefficient is defined as the ratio of the rate constants of a reaction at two different temperatures separated by 10 C.
The two temperatures generally taken are 35 C and 25 C. For most homogeneous reactions the value of temperature coefficient lies between 2 and 3.
In some cases, the value of temperature coefficient of the reaction is greater than 3. Effect of Catalyst on Rate of Reaction A catalyst is a substance which alters the rate of chemical reaction and remains unchanged in amount and chemical composition at the end of the reaction.
In most of the reactions, catalyst increases the rate and they are known as positive catalyst. Though there are also some catalyst which decreases the rate of reaction and are rightly so known as negative catalyst. The function of a catalyst is to alter the rate of reaction. Effect of Light on Rate of Reaction Light is a form of energy and it affects the rate of several reactions considerably. For example, the reaction between hydrogen and chlorine at ordinary temperature and in the absence of light is very slow.
But, when the mixture of the two gases is exposed to sun light, the reaction proceeds at a very fast rate and the mixture becomes explosive. Tags Chemistry Science. Facebook Twitter. Follow by Email Get all latest content delivered straight to your inbox. Popular Posts. November 24, Recent Posts. Biology Commerce History Literature Physics. Random Posts. Menu Footer Widget.