A catalyst increases the rate of a reaction by lowering the activation energy so that more reactant molecules collide with enough energy to surmount the smaller energy barrier.

Use of catalyst increases rate of reaction. A catalyst lowers the activation energy and so more particles can attain activation energy, thus a faster rate of reaction. Only a small amount of catalyst is required. Increasing the amount of catalyst used will not increase the rates of reaction beyond a certain point.

When the concentrations of the reactants are raised, the reaction proceeds more quickly. Catalysts can lower the activation energy and increase the reaction rate without being consumed in the reaction.

A catalyst increases the rate of the chemical reactions by decreasing the activation energy of the concerned reactions. When the activation energy is decreased, the chemical reaction can proceed at a faster rate. Hence, the answer is ‘by decreasing the activation energy of a reaction’.

There are four main factors that can affect the reaction rate of a chemical reaction:

• Reactant concentration. Increasing the concentration of one or more reactants will often increase the rate of reaction.
• Physical state of the reactants and surface area.
• Temperature.
• Presence of a catalyst.

Solution : The enthalpy change, ΔH is difference of energy between reactant and product molecules.

The factors which influence the heat of reaction are

• Physical state of reactants and products.
• The temperature of the reaction.
• The method by which the final products are obtained.
• Whether the reaction is carried out at constant pressure or constant temperature.

When solids and liquids react, increasing the surface area of the solid will increase the reaction rate. The reaction rate decreases with a decrease in temperature. Catalysts can lower the activation energy and increase the reaction rate without being consumed in the reaction.

Whereas when we increase the temperature then there is increase in rate of reaction due to increase in kinetic energy of molecules. Thus, we can conclude that decreasing the concentration of the reactant will slow down a reaction.

You can see that as the temperature increases, the value of Kp falls. This is typical of what happens with any equilibrium where the forward reaction is exothermic. Increasing the temperature decreases the value of the equilibrium constant. It will do that by favoring the reaction which absorbs heat.

A fast reaction is therefore best defined as one whose half-life is less than a few seconds (that is, of the same order as the human response time or the mixing time for reactants) at room temperature using conventional reactant concentrations (say 0.1 mol dm -3). They invariably involve free-radical reactions.

The premise of this theory is simple: molecules have to collide to react. Therefore, the speed at which a reaction takes place depends on two main factors: The frequency of collisions: The more often molecules collide with each other, the faster the reaction proceeds.

There are two difficulties with fast reactions. One is that the time that it takes to mix reactants or to change the temperature of the system may be significant in comparison with the half-life, so that the initial time cannot be measured accurately.

Reactions usually slow down as time goes on because of the depletion of the reactants. The rate constant, or the specific rate constant, is the proportionality constant in the equation that expresses the relationship between the rate of a chemical reaction and the concentrations of the reacting substances.

1/t means that the order of reaction is a first order. Meaning that the rate of reaction is directly proportional to reactant concentration. Scientists work with the standard units, therefore 1/t is 1 divide by 1 second.

Typically, reaction rates decrease with time because reactant concentrations decrease as reactants are converted to products. Reaction rates generally increase when reactant concentrations are increased.

If the concentration of A is doubled, the reaction rate will be unchanged, as the reaction is of zero order by A.

The rate of a reaction is a powerful diagnostic tool. By finding out how fast products are made and what causes reactions to slow down we can develop methods to improve production. This information is essential for the large scale manufacture of many chemicals including fertilisers, drugs and household cleaning items.

The average kinetic energy of these particles is also increased. The result is that the particles will collide more frequently, because the particles move around faster and will encounter more reactant particles. However, this is only a minor part of the reason why the rate is increased.

Reactant concentration, the physical state of the reactants, and surface area, temperature, and the presence of a catalyst are the four main factors that affect reaction rate.

A catalyst is a substance that can be added to a reaction to increase the reaction rate without getting consumed in the process. Catalysts typically speed up a reaction by reducing the activation energy or changing the reaction mechanism. Enzymes are proteins that act as catalysts in biochemical reactions.

Explanation: Increasing the concentration of reactants usually increases the frequency of effective collisions between reactant molecule. This also results in the increase in the rate of a reaction .

In the presence of a catalyst, both the forward and reverse reaction rates will speed up equally, thereby allowing the system to reach equilibrium faster. However, it is very important to keep in mind that the addition of a catalyst has no effect whatsoever on the final equilibrium position of the reaction.

According to Le Chatelier’s principle, if pressure is increased, then the equilibrium shifts to the side with the fewer number of moles of gas. For example, if the temperature is increased for an endothermic reaction, essentially a reactant is being added, so the equilibrium shifts toward products.

the energy of the particles increases. the frequency of successful collisions between reactant particles increases.

1 Answer. A catalyst has precisely no effect on the the enthalpy change of a reaction.

WHAT SORT OF WAYS CAN WE MEASURE THE SPEED OF A CHEMICAL REACTION? The phrase ‘rate of reaction’ means ‘how fast or how slow is the reaction’ or ‘the speed of the reaction’. It can be measured as the ‘rate of formation of product’ (e.g. collecting a gaseous product in a syringe) or the ‘rate of removal of reactant’.