A reaction coordinate is a graph that is used to measure the progress of a reaction as reactants are transformed into products. In order for a reaction to take place enough energy must be present in the system overcome the activation energy. The state between products and reactants is called the transition state or activation complex, this is where bonds are being formed and broken. The difference between the locations of product and reactants on the graph show delta H positive if products are above reactants negative if products are below reactants. A particle diagram follows the same concept just with particles. Particles must be properly oriented with the reactants facing each and enough energy must be present for the particles to break bonds of existing compounds to form the new bonds of the product.
Simple compounds are more likely to react then complex molecules. Smaller particles will more likely react then larger particles with higher rates as they move at faster speeds creating more chances to collide. Increasing the molarity of a substance or amount will increase chances and rates of reaction as their is a higher amount of reactants to collide with each other. Increasing temperature increases reaction rate and probability of reacting as particles move at an accelerated rate causing more collisions. Adding a catalyst increases reaction rate and and probability of happening as it lowers activation energy for a reaction allowing reactions to occur at lower energies. Decreasing temperature, molarity or amount or reactants, or increasing particle size will lead to slower and less likely reactions.
In the lab Iron(3) nitrate was mixed with potassium thiocyanide to create a the substance below in a chemical reaction. The diagram would look like this: