1. Title: Reaction Rates Complete the activity listed below
16/07/2019
Lesson aim: Understand the term “rate of reaction” and explain factors that affect the rate of a reaction.
In your own words, describe/explain how we might use the 2 practical set-ups below to monitor how much product is made in a reaction.
Key words: Rate of reaction, reactant, product, collision, limiting reagent, excess.

2. Rate of reaction
16/07/2019
This session is all about explaining the factors that affect the rate of a chemical reaction and calculating rates from data.
Rate of reaction: In simple terms, this is how fast a reaction happens.
In more complicated terms: the speed at which chemical reactants react together and turn into products. This involves reactants colliding with sufficient energy to overcome an activation energy. Reactants that collide with insufficient energy do not react.

3. Collisions, collisions everywhere…
16/07/2019
Some reactants have more energy than others.
More energy means stronger force during collision.
More energy means the reactants move faster – greater collision frequency.
Why are some reactions faster than others?

4. Concentration
16/07/2019
Below are 3 images that represent 3 glasses of orange squash:
In what ways are they the same?
In what ways are they different?

5. Concentration
16/07/2019
Below are 3 images that represent 3 glasses of orange squash:
In what ways are they the same?
In what ways are they different?
All contain orange juice (particles).
But different quantities of orange:water

6. Defining Concentration
16/07/2019
Concentration is the amount of solute dissolved in a solvent (99.9% of the time we will use water as a solvent).
So: 10g dissolved in 100cm3 of water would have a concentration of: 10g/100cm3 = 0.1g/cm3.
Calculate these concentrations:
1) 100g in 100cm3. 2) 5g in 25cm3. 3)340g/50cm3.

7. More successful collisions per second, the faster the rate.
Exam-style wording
16/07/2019
It is the frequency of successful collisions that determines the rate of reaction.
More successful collisions per second, the faster the rate.
A greater concentration increases the number of particles that can collide and react, increasing the number of collisions per second and the rate of reaction..

8. How can we tell if a reaction is happening?
16/07/2019
For reactions that produce gases (and therefore bubble) it is very easy to see whether or not the reaction is faster or slower.
Other ways you could tell:
Rate of temperature change.
Rate of colour change.

9. Changing pressure
16/07/2019
An increase in pressure means you have squashed the particles closer together. This is like increasing concentration: rate increases.
The particles are closer together, therefore more likely to collide.
There is a greater frequency of collisions.
There are more collisions that have enough energy to overcome the activation energy, so the rate of reaction increases.

10. Changing pressure
16/07/2019
A decrease in pressure means you’ve spaced the particles further apart. This is like decreasing concentration: rate decreases.
The particles are further apart, therefore less likely to collide.
There is a lower frequency of collisions.
There are fewer collisions that have enough energy to overcome the activation energy, so the rate of reaction decreases.

11. Temperature and collisions: Describe what you observe!

12. Putting this into words
16/07/2019
You need to be able to describe and explain the animation using the following key terms:
Collision: This is when particle bump into each other.
Frequency: This is how often something happens (per second).
Reactant: This is a chemical that is used in a reaction.
Product: This is a chemical that is made in a reaction.
Activation energy: This is a minimum amount of energy with which reactants must collide for a reaction to start.
Limiting reagent: This is the reactant that runs out first during a reaction – it determines (limits) how long a reaction can last for.

13. Exam-style wording The higher the temperature of the reaction…
16/07/2019
The higher the temperature of the reaction…
The more energy the reactant particles have.
The collision frequency between reactant particles increases…
And more particles have enough energy to overcome the activation energy.
This increases the rate of reaction…
Creating products more quickly.
The reaction stops when the limiting reagent has run out.

14. Surface Area 16/07/2019 3cm x 3cm = 9cm2.
Let’s say each “small square” is 1cm in length.
The big cube has lengths of 3cm.
Each face has an area of:
3cm x 3cm = 9cm2.
A cube x6 faces: 6 x 9cm2 = 54cm2.

15. Surface Area
16/07/2019
That’s all of the smiley face reactants from the previous slide…still space for more?!
We now have 6 faces each of 9cm2 and 12 faces of 3cm2.
The total being 90cm2!!
Whilst the individual pieces are smaller the total surface area has increased. (More sites to react on = greater collision frequency=more successful collisions = faster rate of reaction)

16. Changes in reactants and products
16/07/2019
Changes in reactants and products
[Insert]
Describe what happens to the amount of reactants and the amount of products during the course of a reaction.
As a chemical reaction progresses the amount (concentration) of reactant decreases and the amount (concentration) of product increases. [You can use the curves/data from the graph to as proof).

17. Changes in reactants and products
16/07/2019
Changes in reactants and products
[Insert]
“The rate of a chemical reaction decreases (slows down) the longer the reaction progresses” Use the graph above to try and explain this.
As the reaction proceeds there are fewer reactant molecules and more product molecules.
There will be fewer collisions between reactant particles:
There are fewer reactants to collide together.
There are more product molecules that get in the way/block collisions.

18. Simple rate calculations
16/07/2019
Simple rate calculations
The rate of reaction can be calculated by the following equations:
Use these to calculate the rates for:
150cm3 of carbon dioxide gas is produced over 10 seconds.
5.5g of magnesium oxide are used up in a neutralisation reaction with hydrochloric acid in the first 15 seconds of the reaction.
8g of hydrogen gas are produced over 64 seconds.
150cm3/10s = 15cm3/s
5.5g/15s = 0.367g/s
8g/64s = 0.125g/s