Increasing the concentration of reactants in a chemical reaction generally what?

• A. Decreases the reaction rate
• B. Increases the reaction rate
• C. Has no effect on the rate
• D. Reverses the reaction direction

Answer: (B)

Increasing the concentration of reactants raises the rate because reactions happen when molecules collide. More particles in the same volume means collisions happen more often, so there are more opportunities for successful, energy-able and properly oriented collisions to occur per unit time. This shows up in rate laws: if a reactant appears with a positive exponent, increasing its concentration increases the rate. So, in general, higher reactant concentration leads to a faster reaction. (Note: there are special cases, like zero-order behavior or enzyme saturation, where changing concentration doesn’t change the rate, but those are exceptions to the typical pattern.)