Why do groups among the among the main group elements display similar chemical behavior

Because they have the same electronic structure, in the fact that they have the same number of electrons in their highest energy level, therefore they need to either lose the same or gain the same amount of electrons to become stable.

Heat is involved in chemical change in two ways; chemical changes either result in heat being added to or removed from an object, and chemical changes require a certain amount of heat before they can take place.

Depends on the speed of the car.