Some factors may increase or decrease the speed of a chemical reaction. Are they:
- contact surface
- presence of light
The temperature is linked to the agitation of the molecules. The warmer, the more agitated the molecules become.
Increasing the temperature increases the kinetic energy of the molecules (movement). If the molecules move more, they collide more and more energy, decreasing the activation energy and, consequently, increasing the number of effective collisions. Therefore, the speed of reaction also increases.
For this reason, we increase the flame of the stove for cooking and use the refrigerator to prevent food spoilage.
The contact area between reagents also interferes with the speed of chemical reactions. The larger the contact surface, the greater the number of molecules reacting, the greater the number of effective collisions, and thus the speed of reaction increases.
This explains, for example, why we should take a whole aspirin tablet instead of powder. The powdered tablet reacts faster, causing injuries to our stomach. If it is swallowed whole, it will take longer to react, avoiding injury.
A powdery substance reacts faster than an entire substance because it has a larger contact surface. See other examples:
- meat is more easily digested when chewed than whole;
- twigs burn faster than a piece of wood of the same mass;
Steel wool burns faster than a piece of iron of the same mass.
Pressure is the ratio of force to area, ie to force on a given area. As pressure increases in a container, the volume decreases and thus increases the concentration of reagents. The molecules collide more, increasing the number of collisions and thus increasing the speed of reaction.
Concentration is related to the amount of solute and solvent of a substance. Increasing the concentration of reagents increases the number of reagents molecules, increasing the number of collisions and also increasing the speed of reaction. It is associated with the Kinetic Law (Guldber-Waage Law).
When you increase the oxygen concentration in a burn, combustion happens faster.
Some chemical reactions occur faster when in the presence of light. Light influences the speed of reactions because it is an electromagnetic waveform energy that helps break down the activation energy barrier.
Hydrogen peroxide, for example, decomposes more easily when exposed to light, so we should keep it in a dark place.
Photosynthesis performed by plants is a type of reaction that is influenced by the presence of light. Another reaction where light is widely used is the decomposition of AgBr, which gives rise to photographic films.