Rates of reaction

Question 1

What is the rate of a chemical reaction?

Answer 1

• how fast the reactants are changed into products

Question 2

What is an example of a moderate speed reaction?

Answer 2

• metal magnesium reacting with an acid to produce a gentle stream of bubbles

Question 3

What does the rate if a chemical reaction depend on?

Answer 3

1- collision frequency of reacting particles
- the more collisions there are the faster the reaction is

2- energy transferred during a collision
- particles have to collide with enough energy for the collision to be successful

Question 4

What is activation energy?

Answer 4

• minimum amount of energy that particles need

Question 5

Why do particles need activation energy?

Answer 5

• particles need this much energy to break the bonds in the reactants and start the reaction

Question 6

What is the four things that affect rate of reaction?

Answer 6

• temperature
• concentration of a solution or the pressure of a gas
• surface area
• catalyst

Question 7

How does increasing temperature increase rate of reaction?

Answer 7

• when temperature is increased particles move faster
• so they have more collisions
  -higher temperature increases energy of the collisions because the particles are moving faster
• reactions only happen if the particles collide with enough energy
• so at higher temperatures there will be more successful collisions
• so increasing temp increases rate of reaction

Question 8

How does increasing concentration (or pressure) in a solution increase rate of reaction?

Answer 8

• if a solution is made more concentrated it means there are more particles of reactant in the same volume
• this makes collisions more likely
• so reaction rate increases

Question 8

How does increasing concentration (or pressure) in a gas increase rate of reaction?

Answer 8

• increasing pressure means that the particles are more crowded
• the frequency of the collisions between particles will increase
• so rate of reaction will also increase

Question 9

How does surface area (smaller solid particles) affect rate of reaction?

Answer 9

• breaking a solid into smaller pieces will increase surface area to volume ratio
• more solid exposed
• particles around it will have more area to work on
• so frequency of collisions will increase
• rate of reaction is faster for solids with a larger surface area to volume ratio

Question 10

What is a catalyst?

Answer 10

• substance which increases rate of reaction without being chemically changed or used up in the reaction

Question 11

How do catalysts work?

Answer 11

• decreases activation energy needed for a reaction to occur
• they do this by providing an alternate reaction pathway that has lower activation energy

Question 12

How can you calculate rate of reaction?

Answer 12

rate of reaction= amount of reactant used or amount of product formed/time

Question 13

How can you do a precipitation reaction to find rate of reaction?

Answer 13

• mix two see through solutions
• producing a precipitate which clouds the solution
• mix the two reactant solutions and put the flask on a piece of paper that has a mark on it
• observe the mark through the mixture and measure how long it takes for the mark to be obscured
• the faster it disappears the faster the rate of reaction

Question 14

How can you find the rate of reaction with the change in mass experiment?

Answer 14

• as the gas is released the lost mass is easily measured on the balance
• the quicker the reading on the balance drops, the faster the rate of reaction
• you know the reaction has finished when the reading on the balance stops changing
• do experiment in fume cupboard

Question 15

How can you find the rate of reaction with the volume of gas given off experiment?

Answer 15

• involves using a gas syringe to measure volume of gas given off
• more gas given off during a set time interval, the faster the rate of reaction
• you can tell when the reaction is finished when no more gas is produced
• plot a graph of gas volume against time elapsed

Question 16

How can you measure how surface area affects rate of reaction?

Answer 16

• measure volume of gas produced using a gas syringe
• take readings at regular time intervals
• repeat experiment with the same volume/concentration of acid and the same mass of marble chips, but with the marble chips more crunched up
• repeat with the same mass of powdered chalk

Question 17

What is a experiment to show how reaction rate is affected by temperature?

Answer 17

• sodium thiosulfate and hydrochloric acid are both clear solutions
• but they react together to form a yellow precipitate of sulfur
• measure rate by watching a black mark disappear through cloudy sulfur and timing how long it takes to go
• reaction can be repeated for solutions at different temperatures
• the best way is to use a water bath to heat both solutions to the right temp before you mix them

Question 18

What does the temperature rate of reaction show?

Answer 18

• higher the temp the quicker the reaction
• therefore, the less time it takes for the mark to disappear

Question 19

What is the decomposition of hydrogen peroxide?

Answer 19

• 2H20 = 2H20 + 02

Question 20

What are some examples of catalysts that can be used?

Answer 20

• manganese oxide, copper (ii) oxide, zinc oxide

Question 21

What is the method with a catalyst?

Answer 21

• add some mno2 powder to the h2o2
• measure volume of gas produced at regular time intervals
• record results
• repeat experiment with exactly the same volume/concentration of hydrogen peroxide but using a different catalyst