With the concept of "speed" usually encountered in the course of physics.As a general definition, the speed is a value that shows how the per unit time changes any characteristics.
chemicals used in the definition of "chemical reaction rate."This classification determines how the unit time is changed or the concentration of the initial reactants of the reaction products obtained.
To estimate the speed, change the concentration of one of the substances.
most interesting processes in a homogeneous medium.Homogeneity (homogeneous) systems are liquids or gases.These reactions occur in its entirety.The chemical reaction rate for such a system to calculate the ratio of change of concentration and time interval over which this reaction occurs.
Heterogeneous (heterogeneous) system are as follows: solid - gas, solid - liquid, gas - liquid.In these systems, reactions occur on the surface of the phase boundary.The rate of chemical reactions for inhomogeneous systems determines the number of moles of substances that have joined or formed as a result of exposure per unit area per unit time.
Factors affecting the rate of chemical reaction
on responsiveness affects the concentration of the substances, the temperature, the presence of a catalyst (inhibitor), the contact area and the nature of the active ingredients.
First, the chemical reaction rate is dependent on the concentration of the reactants.It grows in direct proportion to the product of their concentrations.The reason for increasing the speed of increase in the number of collisions acts particle reagents by increasing their number per unit volume.
The increase in the rate of the chemical process contributes to the increase in temperature.Chemical reactions in homogeneous systems (liquid solutions, a mixture of gases), are due to the collision of the components (particles).However, not always a clash of reagents leads to new products.Only active particles which have increased energy, capable of carrying out a chemical reaction.
When the temperature increases the kinetic energy of the chemical species and the number of active particles also increases.Therefore, at high temperatures, the reactions take place faster than at low.Determine how the rate of reaction depends on the temperature, generally allows van't Hoff.This postulate that the temperature increases at every ten degrees Celsius, the chemical reaction rate increases by 3-4 times.However, this rule gives approximate values, and it is used only for initial assessment of the impact of the estimated temperature.
big influence on the speed of reaction has the presence of a catalyst - a substance that accelerates a chemical process.The catalysts react with the reactants to form chemical intermediates, and in the end of the reaction, they are released.The state of aggregation distinguish homogeneous and heterogeneous catalysts.
substances that slow down the reaction are called inhibitors.
chemical reaction rate also depends on the joint area of contact of the reactants.To increase this feature, the substances are ground.The maximum degree of comminution is achieved by dissolving the reagents.Therefore, the fastest reactions occur in solution.
Nature reactants also influences the rate of reaction.For example, iron and magnesium have different rates by reacting with an acid of the same concentration.This is due to the different chemical reactivity of these metals.
