If you double the concentration of a solution while keeping volume and temperature the same, what happens to the rate?

• A. It increases
• B. It decreases
• C. It remains the same
• D. It becomes zero

Answer: (A)

Collision theory shows that how fast a reaction goes depends on how often reacting particles meet with enough energy. When you keep volume and temperature the same but double the amount of particles in that space, you pack more particles into the same volume. That increases the frequency of collisions, so there are more successful reactions per second. Since the temperature is unchanged, the rate constant stays the same, so the overall rate goes up because there are more collisions occurring. In short, doubling concentration makes the rate increase.