Rate of Reaction

Question 1

What is the “activation energy?”

Answer 1

• Activation energy is the minimum amount of energy required for a reaction to occur/ for a succesful collision.

Question 2

What is the idea of collision theory?

Answer 2

• In order for a reaction to occur, particles must collide with sufficient energy.

Question 3

Explain why most collisions do not lead to a
reaction.

Answer 3

• Because a lot of the particles don’t have sufficient kinetic energy (ie. don’t have activation energy.)
• It’s rare for the particles to collide in the right direction.

Question 4

How do you calculate the rate of reaction?

Answer 4

Amount of product used or reactant made/ time

Question 5

Def of rate of reaction

Answer 5

• Change of concentration/ of product or reactant per unit time.

Question 6

What main factors affect the rate of reaction?

Answer 6

1.) Temperature
2.) Concentration
3.) Pressure
4.) Presence of a catalyst.

Question 7

Why does increase in temperature increase the rate of reaction?

Answer 7

• Increased frequency of succesful collisions between particles per unit time as particles have more kinetic energy.
• More energetic collisions as particles have more kinetic energy.

Question 8

How does increase in pressure of gases affect the rate of reaction?

Answer 8

• Increased pressure increases rate of reaction.
• Molecules are closer together so increased frequency of succesful collisions per unit time- increasing rate of reaction.

Question 9

How does increasing concentration affect the rate of reaction?

Answer 9

• Increased conc = increased reaction.
• More particles per unit volume so increased frequency of succesful collisions per unit time - increasing the rate of reaction.

Question 10

What is a catlayst?

Answer 10

• A catalyst is a substance that increases the rate of a chemical reaction without being changed in chemical composition or amount (ie. the catalyst isn’t used up/ is unchanged at end of reaction)

() - extra info for clarification.

SPEC DEFINITION

Question 11

How do catalysts actually increase the rate of reactions?

Answer 11

• Provide an alternative route for reaction to take place, with a lower activation energy.

Question 12

Why are catalysts very useful in industrial reactions?

Answer 12

• Will increase the rate of reactions.
• Will mean reactions can occur at lower temperatures, saving energy and money.

Question 13

What does energy profile look like w/ catalyst vs without?

Answer 13

• Without catalyst: activation energy is a lot larger (peaks higher.)
• W/ catalyst: activation energy is a lot smaller (peaks lower down.)

Question 14

3 different ways rate of reaction can be measured from experiments.

Answer 14

• How long it takes precipitate to form.
• Amount of mass lost
• Volume of gas produced

Question 15

How would you determine rate of reaction from volume of gas produced?

Answer 15

• Attach gas syringe to a conical flask with a bung (with reaction within the flask) and measure volume of gas collected in gas syringe over specified time.

Question 16

How would you determine rate of reaction from how long it takes for precipitate to form? Issue with this set up? How can we reduce this issue?

Answer 16

• Place conical flask (with reaction within it) on paper.
• Start stopwatch and time how long it takes for the cross to disappear (ie. time it takes for precipitate to form.)
• Subjective WHEN cross disappears, depends on eye-sight. Try to use same observer to reduce errors

Question 17

How would you determine rate of reaction from amount of mass lost? Issue with this set up? How to reduce this issue?

Answer 17

• Can be used for reactions that release a gas.
• Place beaker with reactants on balance (measure initial mass.) After specified time, record mass again after. Subtract values to obtain mass of gas lost.
• Issue is production of toxic gases from reaction. Use a fume cupboard if gas is toxic/ harmful.

Question 18

Write equation for reaction between sodium thiosulphate and hydrochloric acid - inlcude state symbols.

Answer 18

Na2S2O3(aq) + 2HCl(aq) → 2NaCl(aq) + SO2(g) + S(s)