The rate and extent of chemical change

Question 1

what is rate

Answer 1

how fast the reactants are changes into products

Question 2

what do particles have to do to make a collision succesful

Answer 2

collide with enough energy

Question 3

activation energy

Answer 3

minimum amount of energy that particles need to react to break the bonds in the reactants and start the reaction

Question 4

what does rate of reaction depend on

Answer 4

• temperature
• concentration of solution
• pressure of gas
• surface area
• prescence of catalyst

Question 5

what do we want to increase to increase rate of reaction

Answer 5

number of successful collisions between reacting particles

Question 6

how do catalysts work

Answer 6

they decrease the activation energy needed for different reactions to occur by providing an alternative reaction pathway with a lower activation energy

Question 7

what are enzymes

Answer 7

biological catalyst that catalyse reactions in living things

Question 8

practical: precipitation and colour change

Answer 8

1. record visual change if initial solution is transparant and product is a precipitate which clouds the solution
2. observe a mark through the solution and the faster the mark dissapears the quicker the reaction
3. if reactants are coloured and products are colourless you can time how long it takes to loose colour (vise versa if reactants colourless and products coloured)
4. However results are subjective and can vary person to person
5. Because of this you cannot plot a rate of reacton graph from these results

• sodium thiosulfate and HCl
• both are clear and react together to form a yello precipitate of sulfur
• put flaks on piece of paper with black cross add dilute sodium thiosulfate then dilute HCl
• time how long it takes for cross to dissapear
• experiment with concentration of acid

Question 9

practical: change in mass

Answer 9

1. mass is usually lost due to gas being given off
2. as gas is release mass disappearing is measured on the balance
3. quicker the reading drops the faster the reaction
4. can take measurements at regular intervasl and plot a rate of reaction graph
5. very (most) accurate as the mass balance is vert accurate
6. however it does release gas straight into the room

Question 10

practical: volume of gas given off

Answer 10

1. use gas syringe to measure gas given off
2. more gas given off = faster reaction
3. usually gas syringes give volumes accurate to the nearest cm3 so quite accurate
4. take measurements at time regular intervals and plot rate of reaction graph
5. have to be careful as if reaction is too vigorous you could blow plunger out of the end of the syringe

• add dilute hydrochloric acid to conical flask
• add magnesium ribbon and quickly attatch an empty gas syringe to the flask
• start stop watch take readings at regular intervals
• graph with time on X axis and volume of gas produced on Y axis
• can repeat with different concentrations sof acid and variables such as volume of acid or amount of magnesium ans see how rate changes

Question 11

how to find mean rate of reaction on a graph

Answer 11

• find the points you are asked for e.g find mean rate of reaction between 20s and 40s
• calculate the change in Y and change in X
• then divide change in Y by change in X

Question 12

how to find rate of reaction at a particular point

Answer 12

draw a tangent at the point then pick two points on the line that are easy to read and use them to calculate the gradient of the tangent in order to find the rate

Question 13

when can an equilibrium only be reached

Answer 13

in a closed system which ensures that no products or reactants can escape and nothing can get in