Q.How do concentrations of the reactant influence the rate of reaction?

Step 1. By collision theory, a reaction's rate depends on how often reactant molecules collide.

Step 2. A higher concentration means more reactant particles occupy the same volume, so the probability of any two of them meeting and colliding in a given second is greater.

Step 3. This is demonstrated with sodium thiosulphate reacting with HCl at three different thiosulphate concentrations (10, 20, 40 ml diluted to the same total volume): the higher the concentration, the SHORTER the time t for a cross mark to disappear (clouded by precipitated sulphur), and plotting $1/t$ (a direct measure of rate) against concentration gives a clearly rising line. …

Connect concentration's effect on rate directly to collision theory (more particles per volume, more frequent collisions) …

• Stating simply 'higher concentration means higher rate' without the underlying MECHANISM (increased collision frequency) that explains WHY -- th …