In chemistry today we completed an experiment called the disappearing X in which

In chemistry today we
completed an experiment called the disappearing X in which we tested how
increasing the concentration affected the rate of reaction. We combine 0.5M
Hydrochloric Acid with Sodium Thiosulphate to time the rate of reaction. We
also did this for 1M and 2M Hydrochloric Acid. When we tested the 0.5m the rate
of reaction was 42.16 seconds and when we tested 1M the rate of reaction was 13.09
seconds. Our science teacher told us the large time difference was because we
doubled the concentration. But when we double the concentration again 2M Hydrochloric
Acid the reaction rate was only 10.66 seconds. Why was there a large
difference between 0.5M and 1M but only a small difference between 1M and 2M?