Answer:
they speed up
Step-by-step explanation:
if you give more heat to a substance they gain more energy which makes them speed up. if you add more particles to a substance the particles gain more pressure which if inside a container can put more strain on the container
example - a balloon
the more air you put into a balloon, the more likely it is to burst because there are more particles colliding with the sides of the container and there is less space
if you put the balloon under a heat source it is more likely to burst because the heat gives the particles more energy which then makes them collide with the container more as they are moving around more