Factors affecting the rate of chemical reaction

With the notion of "speed" is usually encountered in the course of physics. By definition, speed is a quantity that indicates how a characteristic changes over a time unit.

In chemistry, the definition of "the rate of chemical reaction" is used. This category determines how much per unit of time the concentration of the initial reagents or the products of the reaction changes.

To assess the speed, you must change the concentration of one of the substances.

The processes that occur in a homogeneous medium are most interesting. Homogeneous (homogeneous) systems are liquids or gases. These reactions take place in full. The rate of chemical reaction for such a system is calculated by the ratio of the change in concentration and the time interval during which this reaction occurs.

Inhomogeneous (heterogeneous) systems are represented by the following: solid - gas, solid - liquid, gas - liquid. In these systems, the reactions take place at the surface of the phase boundary. The rate of chemical reactions for heterogeneous systems is determined by the number of moles of substances that have entered or formed as a result of the action on a unit surface per unit time.

Factors affecting the rate of chemical reaction

The speed of the reaction is affected by the concentration of substances, temperature, the presence of a catalyst (inhibitor), the area of contact and the nature of the active substances.

First, the rate of chemical reaction is dependent on the concentration of the reacting components. It grows in direct proportion to the product of their concentrations. The reason for the increase in speed is the increase in the number of collisions of particles of reagents due to an increase in their number per unit volume.

Increase in the rate of the chemical process is facilitated by an increase in the temperature regime. Chemical reactions occurring in homogeneous systems (liquid solutions, gas mixtures) occur due to the collision of components (particles). However, not always the collision of reagents leads to the appearance of new products. Only active particles that have increased energy are able to carry out a chemical reaction.

As the temperature rises, the kinetic energy of the chemical particles increases, and the number of active particles also increases. Therefore, at high temperatures, the reactions occur faster than at low temperatures. Determine how the reaction rate depends on the temperature regime, allows the Van't Hoff rule. This postulate says that with increasing temperature for every ten degrees Celsius, the rate of chemical reaction rises by 3-4 times. However, this rule gives approximate values, and it is used only for an approximate initial estimate of the effect of temperature.

The presence of a catalyst, a substance that accelerates the chemical process, has a large effect on the reaction rate. The catalysts react with the reagents, forming intermediate chemical compounds, and at the end of the reaction they are released. According to the aggregate state , homogeneous and heterogeneous catalysts are distinguished.

Substances that slow down the reaction are called inhibitors.

The rate of chemical reaction also depends on the joint area of contact of the reagents. To increase this characteristic, the substances are ground. The maximum degree of grinding is achieved by dissolving the reagents. Therefore, reactions occur most rapidly in solutions.

The nature of the reagents also affects the reaction rate. For example, iron and magnesium have different rates when interacting with acids of the same concentration. This is due to the different chemical activity of these metals.