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Reactant State
A reaction between two substances will be far quicker if the two substances are both gases. This is because all of the individual molecules that constitute the gas can very quickly mix together. Conversely, two solids will take a far longer time to react because most of the molecules you wish to mix are trapped inside the solid shape. To increase the speed of the reaction, you should change the physical state of the reactants so more molecules can collide.
Temperature
Molecules are in constant motion as their constituent nuclei and electrons move around each other. If you increase the temperature of a reactant, those molecules start to move faster. If you place two reactants together and increase the temperature then the molecules will collide with each other far more regularly than if they were moving slowly. Temperature is also a good way to change a substance̵7;s physical state, like boiling water to create steam. By turning the molecules into a liquid or gas they can mix better.
Concentration and Pressure
The concentration of a chemical will increase the reaction rate because there are more individual molecules included in the solution. Imagine you have a bag with ten marbles in it. If you shake the bag, the marbles will start to collide with one another. If you were to then add another ten marbles and shake the bag, the number of collisions would increase. By increasing the concentration of your liquid solution even further you can continue to speed up the reaction. In a gas, increasing the pressure will have the same effect.
Surface Area
As already explained, a solid reactant will take a long time to react because most of the molecules are inside the solid and not exposed to the second reactant. If, however, you increase the surface area of the solid, then considerably more molecules are exposed. Instead of using a block solid, use a honeycomb shape or flatten the block. Alternatively, grind your solid block into a powder, or shave it into flakes. All of these increase the substance's exposed surface area.
Catalysts
You can also speed up a reaction by adding a third substance, known as a catalyst. If, for example, you wanted to change the monomer ethylene into the polymer polyethylene, you would add a catalyst called benzoyl peroxide. This works by breaking the double carbon bonds in the ethylene so the individual monomers join together in a chain. At the end of the reaction you would be left with polyethylene and the benzoyl peroxide once more. The catalyst is not used up in the reaction but only breaks the bonds that hold molecules together.