physical chem; kinetics

Question 1

what is the collision theory?

Answer 1

states that for a chemical reaction to take place, particles need to collide with correct orientation & enough KE

Question 2

how does ineffective collision affect a chemical reaction?

Answer 2

particles would bounce off without causing a chemical reaction

Question 3

what is the rate of reaction?

Answer 3

the change of conc/amount of a reactant or product per unit time

Question 4

state what happens when reaction rate increases

Answer 4

when more collisions take place the no.of particles with energy greater than Ea increases

Question 5

what is activation energy?

Answer 5

it’s the minimum amount of energy required to required for reaction to occur

Question 6

how does Ea affect chemical reactions?

Answer 6

for a reaction to take place particles need to overcome Ea

Question 7

what is a catalyst & how does it affect the reaction rate?

Answer 7

a catalyst is a substance that increases the rate of reaction without being used up by providing an alternative pathway

Question 8

how is the rate of reaction calculated?

Answer 8

rate of reaction (mol dm-3 s-1) = change in amount of reactants or products (mol dm-3 ) ÷ time (s)

Question 9

what does the maxwell boltzmann distribution show?

Answer 9

shows the energy in gas particles

Question 10

how does temp affect rate?

Answer 10

when temp increases the particles gain more KE = a larger proportion of particles will have energy greater than Ea

when temp decreases = a smaller proportion of molecules will have energy greater than Ea

Question 11

how are the effects of temp shown on a maxwell boltzmann distribution graph?

Answer 11

increased temp:
curve sits on the right
peak is lower
are under the curve is the same
area under curve beyond Ea increases

decreased temp:
curve sits on the left
peak is higher
area under curve is the same
area under the curve beyond Ea decreases

Question 12

why do we get a faster rate of reaction when temp is increased?

Answer 12

as particles move around more at higher temps - they collide more often = reactions happen faster

Question 13

how does conc affect rate?

Answer 13

increasing conc = increases rate
as particles closer together & collide more often - higher chance of reaction

Question 14

how does pressure affect rate?

Answer 14

increasing pressure = increases rate
as particles are closer together & collide more often - higher chance of reaction

Question 15

why are catalysts used in reactions?

Answer 15

to make the products faster & are used to lower the temp required for a reaction which saves energy & money

Question 16

give an example of a catalyst & its features

Answer 16

zeolite
has large SA due to its micro pores in the pellets

Question 17

how are the effects of catalysts shown on the maxwell boltzmann distribution graph?

Answer 17

catalysts lower the Ea so more particles have enough energy to react (dotted Ea line moves to left)

Question 18

how is rate measured in experiments?

Answer 18

1. how long it take for ppt to form
   place a cross on paper & time how long it takes for the cross to disappear (ppt to form) - use same observer to reduce errors as it’s difficult to know when exactly the cross disappears
2. amount of mass lost
   for reactions that produce gas - place reaction on balance & measure the mass loss as gas is lost
   use fume cupboard if gas is harmful/toxic
3. vol of gas produced
   measure amount of gas produced using a gas syringe over a specified time