4.1 Rates of Reactions

Question 1

Activation Energy

Answer 1

The required energy that particles need to react, if particles don’t have this energy, they will just rebound and remain unchanged

Question 2

Collision Frequency

Answer 2

How often do particles collide with each other?

Question 3

Percentage success

Answer 3

What percentage of the collisions have enough energy?

Question 4

Factors effecting rate of reaction

Answer 4

• Surface Area
• Temperature
• Catalysts
• Concentration/Pressure

Question 5

Surface area, Rate

Answer 5

• Increasing surface area increases rate of reaction
• As more of the solid is exposed to particles
• Meaning the collision frequency is higher
• So there are more successful collisions per unit time

Question 6

Concentration/Pressure, Rate

Answer 6

• Higher solution concentration/gas pressure increases rate of reaction
• As there are more particles per unit volume
• Meaning collision frequency is higher
• Meaning more successful collisions per unit time

Question 7

Temperature, Rate

Answer 7

• Increase temperature increases rate of reaction
• As the particles have more kinetic energy
• Meaning the percentage of collisions with enough energy is higher
• Meaning more successful collisions per unit time

Question 8

Catalysts, Rate

Answer 8

• Presence of a catalyst increase rate of reaction
• As they provide an alternate route with a lower activation energy
• So the percentage of collisions with enough activation energy is higher
• Meaning more successful collisions per unit time

Question 9

How do you increase surface area?

Answer 9

Cut or grind up solid, smaller prices = higher surface area

Question 10

Marble Chip Experiment

Answer 10

• The effect of surface area on rate is usually measured by reacting calcium carbonate chips and hydrochloric acid
• Higher surface area = more gas produced in 10s (not overall)
• Gas Syringe

Question 11

Equation for Marble Chip Experiment

Answer 11

CaCO3 (s) + 2HCl —> CaCl2(aq) + H2O(l) + CO2(g)

Question 12

Marble Chip Experiment Variables

Answer 12

Input: Different sizes of chips
Output: Amount of gas produced
Controls: Temp, Mass of CaCO3, Volume and Conc of HCl

Question 13

Marble Chip Experiment Graph

Answer 13

• Higher Surface Area = Steeper line

- Same final volume as amount of reactants has not changed

Question 14

Rate of Reaction Equation

Answer 14

Rate = Change in reactant or product/time taken

Question 15

Disappearing across Experiment

Answer 15

• The effect of concentration is usually demonstrated by reacting sodium thiosulphate solution with Hydrochloric Acid
• Sulphur is slowly produced and you can’t see through mixture after a while

Question 16

Equation for disappearing cross experiment

Answer 16

Na2S2O3 + 2HCl —> 2NaCl + S + SO2 + H2O

Question 17

Disappearing Cross Experiment Variables

Answer 17

Input: Concentration is Sodium Thiosulphate
Output: time taken for cross to disappear
Controls: Total volume, Concentration of HCl, Temp

rate = 1/time

Question 18

Disappearing Cross Experiment Results

Answer 18

• Graph shows a straight line, meaning it’s directly proportional
• Meaning double concentration, doubles rate of reaction

Question 19

Magnesium and Acid Experiment

Answer 19

• This experiment is used to show the effect of temperature by reacting magnesium and hydrochloric acid
• Heat HCl until magnesium dissapears

Question 20

Magnesium and Acid Experiment Equation

Answer 20

Mg + 2HCl —> MgCl2 + H2

Question 21

Magnesium and Acid Experiment Variables

Answer 21

Input: Temp of HCl
Output: Time taken for Mg to disappear
Controls: Mass & SA of magnesium, Volume and conc of HCl

Question 22

Magnesium and Acid Experiment Results

Answer 22

• Not directly proportional, not a straight line

- Doesn’t go through origin because rate isn’t 0 and 0 degrees

Question 23

What are catalysts?

Answer 23

• Increase Rate

- Remain Chemically Unchanged

Question 24

How do catalysts work?

Answer 24

-Provide an alternate route with lower activation energy

Question 25

Hydrogen Peroxide Experiment

Answer 25

• Shows the effect of catalysts using the decomposition of hydrogen peroxide
• The reaction is normally very slow but is catalysed by manganese oxide
• Use different catalysts

Question 26

Hydrogen Peroxide Experiment Equation

Answer 26

2H2O2 —> 2H2O + O2

-The catalyst is not in the equation as it’s unchanged

Question 27

Colour of manganese oxide

Answer 27

Black Solid

Question 28

Hydrogen Peroxide Experiment Variables

Answer 28

Input: Which catalyst is used
Output: Volume of O2
Controls: Temp, Mass and SA of mg, Conc and Vol of H2O2

Question 29

Hydrogen Peroxide Experiment Results

Answer 29

• More effective catalysts increase rate more effectively (steeper line)
• All lines flatten out eventually

Question 30

Disappearing Cross

Answer 30

Used to show when a material is formed and makes liquid opaque

Question 31

Gas Syringe

Answer 31

Measures amount of gas produced, very accurate and easy to read, gas could leak or move too quickly

Question 32

Mass lost

Answer 32

Measures how much mass has left the conical flask (gas), easy to set up, could lose gas before timer starts

Question 33

Collecting gas underwater

Answer 33

Measures amount of gas produced, can get easy readings, gas may dissolve or leak, hard to read