Rate Of Reaction

Question 1

Collision Theory

Answer 1

Two particles can only react when they collide with sufficient energy ( activation energy Ea)

Question 2

Factor: Pressure

Answer 2

How to increase (gases):
• Smaller container
•Adding more particles

Result:
•More particles per unit volume
•More frequent collisions
•Increasing frequency of successful collisions (raising rate of reaction)

Question 3

Factor: Surface Area

Answer 3

Increased by (solids):
•Cutting up/powder of solids allows for larger number of reaction sites (SA)

Result:
•Increased frequency of collisions (collisions per unit time)
•Increased frequency of successful collisions (increased rate of reaction)

Question 4

Factor: Concentration

Answer 4

• Only solutions

Result:
•More particles per unit volume ( g/dm or moles/dm)
• Increased frequency of collisions
• Increased frequency of successful collisions (increased rate of reaction)

Question 5

Factor: Temperature

Answer 5

Increase means :
•Increased average internal kinetic energy (increased speed of particles)

Result:
•Higher speed=more frequent collisions
•Higher energy=more successful collisions above Ea

Question 6

Factor: Catalysts

Answer 6

What they do:
• Provide alternative reaction pathway with lower Ea

Result:
•Greater number of particles above Ea
•More frequent successful collisions

Question 7

Monitoring Rate of Reaction:
3 Reaction-completion threshold method

Answer 7

•For precipitation reactions of clear solutions

Method:
•Time how long it takes for solution to become cloudy with products and cross is no longer visible

Result:
•Gives a single piece of data (no graph)
•Shows length (time) of reactions

Question 8

Measuring Rate of Reaction:
Mass-loss/gain Method

Answer 8

Mass-loss:
•Mass of solid will reduce as gas is released and recording it creates a rate graph

Mass-gain:
•Reactions that form oxides gain mass
•Measure mass of crucible with and without reactant and lid (starting mass)
•Measuring the mass at intervals until a constant value creates a rate curve

Question 9

Measuring Rate of Reaction:
Gas Collection Method

Answer 9

Low solubility Gases:
•Measuring cylinder and delivery tube
•Gas displaces water into cylinder and allows us to record volume produced by reaction
•Time for rate curve

Soluble Gases:
•Gas syringe + reaction flask
•Gas is collected by syringe
•Measuring at intervals gives volume and time for rate of reaction graph

Question 10

Endothermic Reactions

Answer 10

•Take in energy from surroundings
•Positive change in enthalpy
•Chem Energy is breaking bonds then releasing into surroundings afterwards
•Temperature decreases
•Bond breaking is always endothermic
(eg.) -Melting
-Boiling
-Thermal Decomposition
-Photosynthesis

Question 11

Exothermic Reactions

Answer 11

•Give out heat energy to surroundings
•Less chem energy in products than reactants (negative enthalpy)
•Temperature increases
•Bond formation is always exothermic
•Need Ea to be supplied

(eg.) -Condensing
-Freezing
-Radioactive decay