Rate of Chemical Reaction

Subject: Science

Overview

Chemical reactions occur at different rates, with reactant and product concentrations varying with time. Factors affecting the rate of chemical reactions include catalysts, temperature, pressure, surface area, and light. Positive catalysts accelerate reactions, while negative catalysts slow them down. Increased pressure, a larger surface area, and light also affect reaction speed.

Different chemical reactions occur at different rates. While some reactions happen quickly, others happen slowly. For instance, the iron rusts slowly, whereas the interaction between an acid and a base happens quickly. Therefore, the rate of any chemical reaction is defined as the amount of reactants to products that occur per unit of time. Reactant concentrations are at their maximum and product concentrations are at zero during the early stages of a reaction since no product has yet to develop. The concentration of reactants decreases and the concentration of the product increases as soon as the reaction begins. As a result, during a chemical reaction, the concentrations of the reactants and products vary with time.

Factors Affecting the Rate of Chemical Reaction

  1. Catalyst
    A catalyst is a material that changes the pace at which a chemical reaction occurs. Although these compounds alter the velocity of a chemical reaction, the changes they undergo are not permanent. Positive catalysts are those that accelerate the rate of reaction. Positive catalysts include iron (Fe), manganese dioxide (MnO2), vanadium pentoxide (V2O5), and others. In a similar vein, a catalyst that slows down a chemical process is referred to as a negative catalyst. One example of a negative catalyst is phosphoric acid (H3PO4).
    2KClO3 \(\xrightarrow {MnO_2}\) 2KCl + 3O2
    [MnO2 is a positive catalyst.]
    2H2O2 \(\xrightarrow {H_3PO_4}\) 2H2O + O2
    [H3PO4 is negative catalyst.]
     
  2. Heat
    In general, as the temperature rises, so does the pace of chemical reactions.
    2KClO3 \(\xrightarrow {Heat}\) 2KCl + 3O2
     
  3. Pressure
    During a chemical reaction, the pressure of the gases affects how quickly they react. In general, when the pressure of the gases increases, so does the rate of reaction. Therefore, when the pressure is higher, the response happens faster.
    N2(g) + 3H2(g) \(\xrightarrow {200-900\:atm}\) 2NH3(g)
     
  4. Surface Area
    The rate of reaction increases with decreasing reactant surface area of contact.In a similar vein, a greater rate of reaction results from a larger reactant surface area of contact.
     
  5. Light
    Light is necessary for some chemical reactions. Light quickens the response's pace.
    6CO2 (carbon dioxide) + 6H2O (water) \(\xrightarrow {chlorophyll}\) C6H12O6 (glucose) + 6O2 (oxygen)
    2AgNO3 (silver nitrate) \(\xrightarrow {light}\) 2NO2 (nitrogen dioxide) + O2 (oxygen) + 2Ag (silver)
Things to remember
  • ​​​​​The ratio of reactants to products that occurs per unit of time determines the rate of a reaction.
  • As the reaction begins, the concentration of reactants decreases and the concentration of products increases.
  • Factors affecting the rate of chemical reactions include catalysts, such as iron, manganese dioxide, and vanadium pentoxide, which accelerate or slow down the reaction.
  • Temperature also affects the rate of reaction, with higher temperatures causing faster reactions.
  • Pressure also affects the reaction, with higher pressure causing faster reactions.
  • Surface area also influences the rate of reaction, with larger areas resulting in faster reactions.
  • Light is essential for some chemical reactions, as it accelerates the response's pace.

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