Topic 6 - chemical change

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 SLOW chemical reaction ?

Answer 2

iron rusting

chemical weathering

Question 3

what is an example of a MODERATE SPEED chemical reaction ?

Answer 3

magnesium and acid

Question 4

what is an example of a fast reaction

Answer 4

burning

an explosion

Question 5

what is the collision frequency ?

Answer 5

how often particles collide

the more collisions the faster the reaction

Question 6

what means a collision is successful ?

Answer 6

when particles collide with enough energy

Question 7

what is the activation energy ?

Answer 7

the minimum amount of energy that particles need to react

Question 8

what does rate depend on ?

Answer 8

• temperature
• concentration
• pressure
• surface area
• presence of a catalyst

Question 9

how does temperature increase rate?

Answer 9

• as temperature increases particles move faster
• meaning they collide more frequently
• it also means that particles have more energy
• so more collisions will have more energy 1

Question 10

how does increasing concentration increase rate ?

Answer 10

• a higher concentration means there are more particles in the same volume
• this increases the frequency of collisions

Question 11

how does increasing pressure increase rate ?

Answer 11

• a high pressure means there is the same amount of particles in a smaller volume
• this increases the frequency of collisions

Question 12

how does increasing surface area increase rate ?

Answer 12

• increase surface area : volume
• this means the sane volume of solid will have more area to work on
• so it increases the frequency of collisions

Question 13

hoe does a catalyst increase rate ?

Answer 13

• a catalyst decreases the activation energy

- this is done by providing alternate reaction pathways

Question 14

what is the equation for rate of reaction ?

Answer 14

amount of reactant used or amount of product formed / time

Question 15

what is the unit of rate ?

Answer 15

cm^3/s
g/s
mols/s

Question 16

what are the experiments to investigate rate ?

Answer 16

• precipitation and colour change
• change in mass
• the volume of gas given off

Question 17

what is produced when magnesium and HCL react ?

Answer 17

hydrogen

Question 18

what is the investigation for concentration ?

Answer 18

• 25cm^3 of dilute sodium thiosulfate to a conical flask
• draw a dark black cross acoss a post- it note
• put the conical flask on the post it note
• add 0.5 mol/dm^3 of HCL and start a stop watch
• stop the stop watch when the cross can no longer be seen
• redo the experiment with the same volume and concentration of sodium thiosulfate but increasing the concentration of HCL by 0.5 each repetition
• WELL VENTILATED AREA

Question 19

what is equilibrium ?

Answer 19

when the forwards reaction is equal to the backwards reaction - SAME RATE

Question 20

what is dynamic equilibrium ?

Answer 20

• concentration and products have reached a balance and won’t change

Question 21

what does it mean if the equilibrium lies to the left ?

Answer 21

the concentration of the REACTANT is GREATER than the PRODUCT

Question 22

what does it mean if equilibrium lies to the right ?

Answer 22

the concentration of the PRODUCT is GREATER than the REACTANT

Question 23

what do the position of equilibrium depend on ?

Answer 23

• temperature
• pressure
• concentration

Question 24

what is Le Chantelier’s principle ?

Answer 24

the idea that if you change the conditions of a reversible reaction at equilibrium the system will try counteract that change
- can be used to predict the effect