Year 11 Chemistry Module 3.3

Rates of reactions

What is a catalyst?

A substance that speeds up a chemical reaction by lowering the required activation energy

What is the collision theory?

The theory that states that for a chemical reaction to occur, reacting particles must collide with one another.

What is molecular orientation?

Refers to the spatial alignment of reactant molecules when they collide. For a chemical reaction to occur, molecules must possess sufficient kinetic energy and collide in the correct geometric orientation so that the reactive atoms can effectively break old bonds and form new ones.

What is activation energy?

The minimum amount of energy required to initiate a chemical reaction

What are effective collisions?

Molecular collisions that successfully result in a chemical reaction. For a collision to be effective, reactant particles must have sufficient energy to break existing bonds (meeting or exceeding activation energy) and collide at the correct spatial orientation to form new bonds

What is reaction rate?

Measures how quickly reactants are consumed or products are formed over time. Otherwise defined as change in concentration of a reactant or a product divided by the time taken for the change

What is the formula/units for rate of reaction?

Change of concentration of substance (litres) divided by time taken (seconds)

As a reaction occurs, do the concentration of reactants decrease or increase?

Reactants concentration decreases

As a reaction occurs, do the concentration of products decrease or increase?

Products concentration increases

What is one way you can determine the rate of reactants for a given length of time?

Plotting a graph where time is on the x axis and concentration of reactant is on the y axis whereby a curve is obtained.

What are different factors that affect the rate of a reaction?

Concentration of reactant, pressure of a gaseous element, temperature of reaction, particle size/surface area, and catalysts

When the concentration of the reactants in a reaction increase, what will there be an increase in? (hint: nothing to do with the products in this context)

An increase in the number of reacting particles per unit volume

When the temperature of a reaction increases, the reacting particles … what?

the reacting particles possess greater average kinetic energy, resulting in a higher reaction rate with sufficient activation energy contained.

How does particle size/surface area of solid reactants increase rate of reaction?

using powdered solid reactants instead of lumps of solid reactants will increase the rate of reaction, as they provide larger accessible surface area for collisions.

What do catalysts do for the reaction rate of a chemical reaction?

for reaction rate, they speed up reaction and lower activation energy

How does an unsuccessful collision take place according to the collision theory?

It will take place if the colliding particles do not have enough energy to reaction

If particles do not have enough energy to collide and therefore react, they may what???

Change into product particles when they collide.

True or false: The different activation energies for different reactions are related to the case with which the bond-breaking and re-forming processes occur.

True: The different activation energies for different reactions are related to the case with which the bond-breaking and re-forming processes occur.

High activation energies are usually associated with reactions in which strong bonds or weak bonds have to be broken?

Strong bonds have to be broken

Even if two molecules collide with sufficient activation energy, there is no guarantee that the collision will be successful, in fact….

Collision theory states that not every collision is successful even if molecules are moving with enough energy.

What do molecules also need to collide with as well as with the right amount of energy?

The right orientation