Chapter 10 Reaction Rates and Equilibrium Flashcards

1
Q

what is rate of reaction

A

change in concentration (of reactants or products) in a given amount of time

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2
Q

what is the rate of reaction formula

A

change in concentration / time

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3
Q

how does rate of reaction change over time and why

A

the starts of very fast because there are lots of reactants so the concentration is very high however it gradually gets slower and slower because you begin to run out of the limiting reagent decreasing the concentration of reactants until the rate of reaction is 0 because the reaction has stopped due to their being no more limiting reagent

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4
Q

what are the three experimental methods to find rate of reaction

A

> use a gas syringe and measure how much gas is produced over time
use a cross and see how long it takes for a precipitate to obscure the cross
Use a pH meter to measure acidity of a solution

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5
Q

how can you find rate of reaction from a graph

A

draw a tangent to the graph at t=0 and the gradient of the tangent is the rate of reaction

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6
Q

what is collision theory

A

reactions occur when reactant particles collide with a certain minimum kinetic energy (activation energy)

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7
Q

what four factors can increase rate of reaction

A

> presence of a catalyst
bigger surface area (solid only)
higher temperature
increased concentration/pressure

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8
Q

what do squared brackets mean [ … ]

A

concentration of …

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9
Q

what do catalysts do

A

they are substances that remain chemically unchanged at end of a reaction but speed up rate of reaction by decreasing activation energy

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10
Q

how do catalysts decrease the activation energy of a reaction

A

they provide an alternative reaction pathway for breaking and making bonds with a lower Ea

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11
Q

what is a homogeneous catalyst

A

catalyst that is in the same physical state as the reactants

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12
Q

how do homogeneous catalysts work

A

they react with reactants to form an intermediate which can then break down to form product and regenerates the catalyst

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13
Q

why are homogeneous catalysts not normally used in industry

A

because you then have to process and separate them from the products

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14
Q

why are homogeneous catalysts not normally used in industry

A

because you then have to process and separate them from the products

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15
Q

how does a heterogeneous catalyst work

A

it provides a surface for which a reaction take place

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16
Q

what are three steps for how heterogeneous catalyst works

A

> reactants form weak adsorptive bonds to surface of catalyst
reaction takes place
the products from the reaction desorb off the surface

17
Q

what is the boltzmann distribution

A

molecules in a sample which are all moving at different speeds/energies

18
Q

what graph is the boltzmann distribution represented on

A

no of molecules of y axis
energy on x axis
curve that has steep incline then peaks before rapidly decreasing a bit then slowly declining for standard boltzmann distribution
dotted line marking activation energy

19
Q

how do catalysts affect the boltzmann distribution

A

the catalyst decreases the activation energy required so shifts the activation energy line closer to the start increasing number of molecules with sufficient energy to react when they collide

20
Q

how does increasing temperature affect the boltzmann distribution

A

increases the number of molecules with sufficient energy so curve increase not as rapidly peaks earlier but then decreases far more gradually

21
Q

what is yield and what is it affected by

A

how much of a substance is produced

affected by the equilibrium and e Chatelier principle

22
Q

what is rate of reaction affected by

A

collision theory

23
Q

what is equilibrium

A

a state of balance where products can be produced and then reverted back into their original reactants

24
Q

what is a dynamic equilibrium

A

reaction where the forward and backwards reaction continually occur at the same rate within a closed system

25
describe an equilibrium that makes a chemist happy
forward reaction is almost complete when equilibrium is established so the equilibrium favours the products/forward reaction
26
describe an equilibrium that makes a sad chemist
few reactants are converted into products when equilibrium is established so the equilibrium position favours the reactants/reverse reaction
27
what is the concentration rule for equilibriums
whether you start with reactants or products you always get the same concentration values for both
28
what is le Chatelier's Principle
if a system is in equilibrium and a change is made in any of the conditions then the system responds to counteract the change as much as possible
29
what are three changes that shift an equilibrium
>adding/removing reactants/products >changing pressure >changing temperature
30
how does adding or removing reactants or products shift the equilibrium
adding a substance shifts the equilibrium away from its side | removing a substance shifts the equilibrium towards its side
31
how does changing pressure shift the equilibrium
increasing pressure shifts the equilibrium towards the side with the least moles of gas decreasing pressure shifts the equilibrium towards the side with the most moles of gas
32
how does changing temperature shift the equilibrium
increasing temperature causes the equilibrium to favour the reaction that is endothermic decreasing the temperature causes the equilibrium to favour the reaction that is exothermic
33
why do catalysts have no affect on the equilibrium
they remain chemically unchanged and lower the activation energy for both reactions
34
what is Kc
the equilibrium constant that is effectively a ratio of products to reactants
35
what is the general equations for equilibriums
aA + bB ⇌ cC + dD
36
what is the general Kc equation
( [C]^c x [D]^d) / ([A]^a x [B]^b)
37
what do different values for Kc mean
Kc = 1 then equilibrium is in the middle Kc < 1 equilibrium favours the reactants Kc > 1 equilibrium favours the products
38
what affects Kc
Amount of substances and pressure have no affect on Kc but changing temperature causes Kc to change