Controlling the Rate

Question 1

Collision Theory

Answer 1

substances can only react with each other if:
-the particles collide with each other
-the collisions have enough energy
-at the correct orientation during collision

Question 2

Kinetic Energy

Answer 2

-also known as the speed of the particles
-when reactants collide they must do so at a speed fast enough to cause the reactants to become product

Question 3

Successful collision

Answer 3

-particles collide with the correct geometry+collide with the correct kinetic energy above or equal to the activation energy.
-The speed of the reaction is dependent on the ratio of successful to unsuccessful collisions per minute. The more successful collision the faster the reaction.
-Example= as the reaction proceed there are fewer reactants, therefore fewer collisions and hence less successful collision, reaction rate decreases towards the end of the reaction

Question 4

How was the concentration of the reactant varied and why

Answer 4

-by changing the volume of the reactant and adding water to keep overall volume constant
-to keep concentration of the other reactants the same/constant so there is only one variable changed

Question 5

Suggest why the procedure adopted to determine the rate of reaction was accurate

Answer 5

colour change is instant to determine end point and not gradual

Question 6

Change of concentration on a graph

Answer 6

-Line going up to the right with no levelling off

Question 7

Activation energy

Answer 7

the minimum kinetic energy particles must have for a successful collision

Question 8

Energy Distribution Graphs

Answer 8

-decreasing activation energy means increasing the area to the right of Ea along the kinetic energy axis.
-an increase in concentration increases the area under the distribution curve. Increasing concentration also increase the height of the graph at all positions, due to more particles present with each kinetic energy.
-more collision=more successful collision, hence the reaction rate increases with increased concentration.

Question 9

How does an increase in concentration affect the rate of reaction

Answer 9

An increase in concentration increases the number of particles equal or above to the activation energy, which means there will be more collisions resulting in more successful collisions with the correct orientation and energy

Question 10

Calculating the relative rate

Answer 10

1 divided by the time, units= s to the minus 1

Question 11

Pressure

Answer 11

increase in pressure increases the rate of reaction due to the decrease in volume thereby increasing the concentration of particles, more collisions occur leading to an increase in rate of reaction.

Question 12

Temperature

Answer 12

-measure of the average kinetic energy of the particles in a substance, which also means it’s the indicator of the speed of the particles
-the higher the temp the greater the kinetic energy of the particles which means there will be more collisions equal or above the activation energy increasing the number of successful collisions

Question 13

why is the beaker dry?

Answer 13

so there would not be any other chemicals present in the beaker, as it can interfere with the concentration

Question 14

why is reaction time less accurate when experiment is carried out at room temp?

Answer 14

hard to determine the end point due to gradual colour change

Question 15

SUMMARY IN GRAPH

Answer 15

-Concentration versus rate in a direct relationship and shows a linear relationship
-Temperature versus rate is a direct relationship but rises exponentially in a graph(since a 10 degree rise doubles the rate)

Question 16

Temperature affects relative rate

Answer 16

-the higher the temp the greater the kinetic energy(higher speed) of the particles results in greater energy during collisions which means there will be more collisions equal or above the activation energy increasing the number of successful collisions

Question 17

Energy Distribution graph TEMPERATURE

Answer 17

-higher temperature graphs are lower and further along=which means more particles who have equal or above energy of activation energy
-molecules above the activation energy have sufficient energy to react/to form an activated complex
-larger area=more successful collisions

Question 18

Particle size

Answer 18

Collisions between particles can only occur on the surface of solid(marble). With smaller particle sizes there is a greater surface area and hence more collisions, increasing number of collisions

Question 19

Description of method using balance

Answer 19

-weigh mass of marble chips
-place everything on balance and weigh
-pour marble into flask and use cotton wool
-start timer and place beaker back onto the balance
-measure everything on the balance every required interval

Question 20

Activated complex

Answer 20

in order to react, the two reactant molecules must first collide. During the collision, the original bonds break and new form. In order to form the products, the reactant must form an intermediate called the ‘activated complex’. This is described as a ‘high energy intermediate between products and reactants’.

Question 21

Activated complex 2.

Answer 21

-activation energy it the additional potential energy which has to be attained by colliding to form an activated complex
-activated complex is unstable arrangement of atoms formed at the maximum of potential energy barrier

Question 22

Exothermic Reaction

Answer 22

release of energy to the surroundings, making the temperature rise(products lower than reactants)

Question 23

Endothermic Reaction

Answer 23

absorption of energy from the surroundings, making temperature fall(products are higher than reactants)

Question 24

Enthalpy Change

Answer 24

is the product P.E-reactant P.E

Question 25

Enthalpy change formulas

Answer 25

E1=products
E2=reactants
E3=point of maximum collision

enthalpy change forward reaction= E1-E2
enthalpy change reverse reaction= E2-E1
activation energy forward reaction= E3-E2
activation energy reverse reaction=E3-E1

Question 26

Catalyst

Answer 26

-a catalyst provides a different reaction pathway to the products. The reactant molecules are first adsorbed onto the surface of the catalyst
-the attraction to the catalyst surface cause molecule A bonds to become weaker. Then molecule B collides with weakened adsorbed molecule A.
-activated complex is easily formed since the molecule A bonds are weaker. This lowers the activation energy
-The product molecules are released from the surface of the catalyst(catalyst lowers activation energy required for successful collisions)

Question 27

Catalyst Poisoning

Answer 27

occurs when the surface of the catalysts becomes contaminated with impurities. Reactant cannot adsorb and then catalyst stops working). If the contaminant is soot(carbon) then burning it off can regenerate the catalyst.

Question 28

Effect of catalyst on graphs

Answer 28

-the catalyst can be also be shown on potential diagrams, it lowers activation energy(hump) and does not affect enthalpy change
-since catalyst lowers activation energy, the area to the right of it increase which increase the number of particles with kinetic energy greater than or equal to activation energy, therefore more collisions can form the activated complex increases rate of reaction.

Question 29

why does the platinum wire not have to be continually heated

Answer 29

it was catalyzing the reaction, so it kept on glowing.