Chemical Changes And Structure #1: Rates Of Reaction

Question 1

Slow reactions

Answer 1

Large particles (lumps), low concentration (dilution), low temperature

Question 2

Fast reactions

Answer 2

Small particles (powder), high concentration, high temperature

Question 3

How do you determine what factor is affecting a chemical reaction?

Answer 3

You must only change one variable at a time

Question 4

What is a variable?

Answer 4

Something that can be changed in a chemical reaction

Question 5

What are some variables?

Answer 5

• temperature
• particle size
• concentration
• volume
• mass

Question 6

How do you carry out a fair test?

Answer 6

By only changing one variable at a time

Question 7

What must happen for a chemical reaction to occur?

Answer 7

The reactants particles must collide

Question 8

How do collisions work?

Answer 8

The collision provides the energy to break the bonds in the reactant molecules and form the new bonds in the product

Question 9

Not all collisions result in…

Answer 9

• A chemical reaction
• Those that do are said to be successful collisions

Question 10

What makes a successful collision?

Answer 10

The particles must collide with:
- the correct geometry (the right angle)
- sufficient energy

Question 11

Any factor which increases the number of collisions between reactant particles will also increase…

Answer 11

The rate of reaction

Question 12

What is the effect of particle size on collision theory?

Answer 12

• As the particle size decreases, the surface area increases
• As the surface area increases, the area available for collisions to happen increases
• This increases the rate of reaction

Question 13

What is the effect of concentration on collision theory?

Answer 13

• As the concentration of reactants increases, there is more particles and so more collisions
• Rate of reaction increases

Question 14

What is the effect of temperature on collision theory?

Answer 14

As the temperature increases:
- the amount of energy a particle has increases
- the faster the particle moves around
- the more likely particles are to collide

the rate of reaction increases

Question 15

All chemical reactions produce…

Answer 15

New substances

Question 16

How can the speed of reaction be measured?

Answer 16

By finding how fast the new substance is formed

Question 17

What are 2 ways we can measure the rate of reaction?

Answer 17

• Measuring a change in mass
• Measuring a change in volume

Question 18

How can we interpret graphs?

Answer 18

• Reactions with more collisions (high conc., high temp., larger surface area / powder) will go to completion/ plateau earlier
• This is because, in these cases, the reactants are used up quicker because there’s more collisions

Question 19

Labelling parts of a graph

Answer 19

A: Reaction rate is fastest. Concentration of reactants is highest.
B: Reaction rate decreases. Concentration decreasing. Reactants being used up.
C: Reaction is finished. All reactants have been converted into products.

Question 20

How do we calculate the average rate of reaction?

Answer 20

From knowing the initial and final quantities and the time interval

Question 21

Average Rate formula

Answer 21

Average rate = change in quantity / change in time

Question 22

What is a catalyst?

Answer 22

• A substance which speeds up the rate of reaction
• Can be recovered chemically unchanged

Question 23

What are 4 ways to speed up a chemical reaction?

Answer 23

• Increasing concentration
• Increasing temperature
• Increasing particle size
• Addition of a catalyst

Question 24

Progress of a chemical reaction means

Answer 24

Rate of reaction

Question 25

How can the volume of gas produced in a reaction be measured?

Answer 25

By using a syringe or upside down measuring cylinder