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 rate, you must change the concentration of one of the substances.
The most interesting are the processes taking place inhomogeneous medium. 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.
Uneven (heterogeneous) systems are representedas follows: solid - gas, solid - liquid, gas - liquid. In these systems, the reactions proceed at the surface of the phase boundary. The rate of chemical reactions for inhomogeneous systems is determined by the number of moles of substances that have entered or formed as a result of the action on a surface unit per unit time.
Factors affecting the rate of chemical reaction
The reaction speed 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 dependentof 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 the particles of reagents due to an increase in their number per unit volume.
Increase the rate of chemical flowprocess is promoted 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 capable of carrying out a chemical reaction.
With increasing temperature, the kineticthe energy of the chemical particles, 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 of 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.
A great influence on the reaction speed hasThe presence of a catalyst - a substance that accelerates the chemical process. 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 onjoint area of contact of 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 speedreaction. 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.
