Heat and molecular motion
Every object is made up of atoms or molecules that are small particles that can not be seen by the eye. These particles are constantly move or oscillate themselves. This is called molecular motion.
The higher the molecular motion, the higher the temperature. The slower the molecular motion, the lower the temperature. Thus, temperature is a physical quantity that shows the active level of molecular motion.
Distribution of particle’s velocity with temperature
Low-temperature gas is mainly distributed on the slower side.
As the temperature of the gas increases, the graph becomes more widespread. And the average speed of the gas also increases.
Why does the chemical reaction get fast when the high temperature?
In order to chemical reactions to proceed, atoms or molecules must collide at a sufficient speed. The higher the temperature, the more gas that reaches the minimum collision speed required for a chemical reaction. Therefore, the higher the temperature, the better the chemical reaction.
And, the low temperature does not mean that the reaction does not occur. Although there is a low probability, there is always the possibility of encountering molecules at high speeds. Therefore, chemical reaction proceeds little by little.
For example, even if water is not heated to 100°C, some water molecules can reach enough speed to escape to water vapor. Some water particles can jump from the water surface to the atmosphere. This is called evaporation.