Chemistry -Chemical reation (PART 1, physical and chemical change, rate of reaction)

Physical change

A change that doesn't produce any new chemical substances, often reversible

Chemical change

A change where new chemical substances are formed and are often diffcult to reverse

What are some signs of chemical change?

Colour change, temperature change, effervescence

What is the collision theory?

In order for a reaction to occur particles must collide with sufficient energy (energy greater than activation energy)

The number of successful collisions depend on…

Number of particles per unit volume, frequency of collisions, kinetic energy of particles and activation energy

How does particle concentration (particles per unit volume) affect successful collisions?

More particles in a given volume mean a higher frequency of successful collisions.

How does frequency of collisions affect successful collisions?

Greater number of collisions per second will give a greater number of successful collisions per second.

How does the kinetic energy of particles affect successful collisions?

Greater kinetic energy mean more collisions exceeding activation energy and higher frequency of collisions

How does activation energy affect successful collisions?

Lower activation energy mean particle collisions need less energy to be successful and therefore more collisions would be successful.

What effect does changing concentration have on reaction rate?

Reaction rate increases when concentration increase

Why does reaction rate increases when concentration increase?

Because they are more particles per unit volume meaning higher frequency of collisions and therefore higher frequency of successful collisions

What effect does changing temp have on reaction rate?

Reaction rate increases with temperature, rate generally doubles for each increase of 10 degrees

Why does Reaction rate increases with temperature?

Because particles move faster, meaning higher frequency of collisions and more particles having enough energy to exceed activation energy

What effect does changing surface area have on reaction rate?

Reaction rate increases when surface area of a solid reactant is increased

Why does reaction rate increase with surface area?

More particles of the solid are exposed, more successful collisions

What effect does adding or removing catalyst (enzymes) have on reaction rate?

Reaction rate increases when catalyst is used

Why does Reaction rate increase when catalyst is used?

Because a catalyst lowers activation energy, particles need less energy to react, more collisions are successful

What effect does changing gas pressure have on reaction rate?

Reaction involving gases goes faster when pressure is increased

Why does Reaction involving gases go faster when pressure is increased?

Because when pressure is increased, concentration is increased, more particles per unit volume, more successful collisions