Unit 3 Quiz - Collision Theory and Reaction Rates

What determines the rate of chemical reactions?

Particle Collisions

What determines the number of particle collisions that take place?

• External conditions such as pressure and temperature, etc.

• number of particles available

• Particle size/surface area

• Energy needed to break existing bonds

What must collisions have in order to destabilize existing bonds and form new bonds?

must have proper orientation(think what particles need to line up for them to be pulled apart)

What must collisions overcome to break bonds?

Activation energy

What is E_a?

The energy needed to produce an “effective collision” to form an activated complex

What does a catalyst do?

It improves the probability of effective collisions by lowering the activation energy

Compare exothermic processes activation energy to endothermic processes

- delta H rxn generally have smaller activation energy barriers compared to + delta H rxn

What is the rate limiting step?

The slow step of a chemical reaction, think of this as traffic on the way to a destination

Where on a reaction curve can you find the reactants?

the curve that decreases/slopes down

Why do reactants decrease throughout a reaction

This is because they are used up as the reaction continues

Where can the products be located on a reaction curve?

the curve sloping up/increasing curve

Where is the activated complex on a exothermic/endothermic reaction curve?

The peak of the curve is the activation complex as the activation energy has been overcome at this point

Where is the necessary activation energy found on exothermic/endothermic reaction curve?

The space(Along the y-axis) from the first line representing the reactants to the activation complex

Where are reactants found on an exothermic/endothermic reaction curve?

the left side of the curve, a flat line

Where are products found on an exothermic/endothermic reaction curve?

One the right side of the curve, a flat line

How can you find the coefficients on compounds in a chemical equation from the reaction curve/data?

By finding the ratio of products to each other, and the ratio of reactants to products, etc.

Why does the slope of the reactants change?

Due to reactants being consumed and fewer effective collisions occuring

equation for rate/slope of reaction curve

(concentration at time 2 - concentration at time 1)/ time 2 -time 1

What does a reaction curve reach when the reaction is finished?

Equilibrium; this is where all the curves “flat-line” and all slopes are constant

What happens if you increase the concentration of reactants?

You increase the reaction rate as there are more particles to easily find each other and react

What happens if you increase pressure?

You increase the reaction rate as the particles are forced into closer proximity and are more likely to react

Are gas reactions faster or slower than liquid reactions?

Gas reactants will react faster than liquid reactants as they have more freedom of movement, and therefore more collisions than liquid particles experience, making them more likely to react

In general, the more reactants the _____ the reaction rate

the faster the reaction rate

What happens if you increase the temperature?

The reaction rate will increase as the particles have more KE and will therefore be more likely to react

What happens if you increase the surface area of reactants?

The reaction rate will increase as there is more contact area for particles to interact, which creates more collisions and therefore a faster reaction rate