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chemistry > reaction rates and equillibrium > Flashcards

reaction rates and equillibrium Flashcards

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1
Q

what is a catalyst

A

a catalyst is a substance which increases the rate of a chemical reaction without undergoing any permanent change itself.

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2
Q

Extra notes on catalysts

A

The catalyst is not used up in the chemical reaction , the catalyst may react with a reactant to form a intermediate or may provide a surface on which the reaction can take place . At the end of the reaction the catalyst is regenerated .

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3
Q

How do catalysts work

A

By providing an alternative reaction pathway with a lower activation energy . This means that a greater proportion of the reactant molecules will collide with enough energy to cross the activation energy barrier and react .

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4
Q

What are the two types of catalyst

A

Homogeneous and heterogeneous catalysts

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5
Q

Is activation energy exo or endo

A

Activation energy is always endothermic

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6
Q

What is another word for physical state

A

Phase

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7
Q

What is a homogeneous catalyst

A

Here the catalyst is in the same physical state as the reactants . The catalyst forms an intermediate which then breaks down to give the product and regenerates the catalyst .

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8
Q

What is a heterogeneous catalyst

A

Here the catalyst is in a different physical state to the reactants . Heterogeneous catalysts are usually solid in contact with gaseous or aqueous reactants eg. In a vehicle catalytic convertor

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9
Q

What is a heterogeneous catalyst

A

Here the catalyst is in a different physical state to the reactants . Heterogeneous catalysts are usually solid in contact with gaseous or aqueous reactants . Eg in a vehicle catalytic convertor

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10
Q

What happens in a heterogeneous catalytic converter

A

Bonds formed to catalyst surface must be weak enough to allow adsorption and desorption to take place , but strong enough to weaken bonds and allow the chemical reaction to take place

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11
Q

What does a poison do

A

Binds to the surface but doesnt leave

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12
Q

What is a catalytic convertor

A

Heterogeneous, adsorption/desorption , three key reactions catalysed

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13
Q

What are the three reactions catalysed

A

The oxidation of carbon monoxide to carbon dioxide .
The reduction of nitrogen monoxide back to nitrogen
The oxidation of hydrocarbons to water and carbon dioxide

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14
Q

What is the equation for the oxidation of carbon monoxide to carbon dioxide

A

2CO(g) + O2(g) —> 2CO2(g)

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15
Q

What is the equation for the reduction of nitrogen monoxide back to nitrogen

A

2NO(g) + 2CO2(g) —> N2(g) + CO2(g)

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16
Q

What is the equation for the oxidation of hydrocarbons to water and carbon dioxide

A

2C6H6+15O2—> 12CO2+ 6H2O

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17
Q

What are the benefits of catalysts

A

-Lower temperatures and pressures required therefore reducing energy demand .
-different reactions can be used with better atom economy thus reducing waste
-lower production costs
-catalysts can be used to generate specific products

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18
Q

What are some examples of important industrial reactions reliant on heterogeneous catalysts

A

Making ammonia (Fe) N2+3H2–> 2NH3
Reforming (fuel improvement ) (pt or rh) c6h14 —> c6h12 +h2
Hydrogenation of alkenes (Ni) c2h4 + h2 —> c2h6
Making sulfur trioxide for sulfuric acid (v205) 2So2 + o2 —> 2so3

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19
Q

what is the general reversible reaction equation

A

aA+bB=cC+dD

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20
Q

what is the general equation for the equilibrium law

A

Kc = [C]c [D]d
[A]a [B]b

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21
Q

what is Kc in terms of reactants and products

A

Kc = products
reactants

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22
Q

what is equilibrium law

A

the exact position of equilibrium is calculated using the equilibrium law

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23
Q

what does the magnitude of Kc indicate

A

the magnitude of Kc indicates the extent of a chemical equilibrium . it indicates how far a reaction proceeds , not how fast

24
Q

when K=1 what does this mean

A

indicates a position of equilibrium that is halfway between reactants and products

25
Q

what does Kc>1 indicate

A

a position of equilibrium that is towards the products

26
Q

what does kc<1 indicate

A

a position that is towards the reactants

27
Q

Suggest two reasons why using a lower temperature is beneficial to the environment

A

Reduction in co2 emissions
Less energy use

28
Q

What are the benefits of catalysts

A

Less co2 emissions as energy is saved
Reduce waste by allowing a different reaction to be used with a better atom economy
Catalytic converters reduce pollution

29
Q

What is the definition for rate of reaction

A

The change in concentration of a reactant or product per unit time

30
Q

What is the equation for rate of reaction

A

Change in concentration of reactant or product / time taken for the change to take place

31
Q

What are the units for rate of reaction

A

Moldm^-3 s^-1

32
Q

Where is the rate of reaction the fastest

A

T=0

33
Q

What are the factors that can affect rate of a reaction

A

Catalyst, temperature, concentration, surface area , pressure

34
Q

What makes a successful collision

A

Head on collision , more energetic reaction takes place
Orientation must be correct

35
Q

how does increasing the concentration affect rate of reaction

A

increases rate of reaction as increases the number of molecules in the same volume , the particles are closer together leading to more frequent collisions

36
Q

how does increasing the pressure affect rate

A

increasing the pressure of gaseous reactants means the same number of molecules occupy less volume so the molecules are closer together and so collide more often

37
Q

what method can we use to measure the rate of reaction for an acid or base

A

ph changes by carrying out titrations
ph changes by using a ph meter/ probe

38
Q

for reactions that produce gases what methods can we use to measure rate

A

change in volume or pressure
the loss of mass of reactants

39
Q

for reactions that produce visual changes what can we observe to measure rate

A

the formation of a precipitate or a colour change

40
Q

for reactions that involve changes in the amounts of ions , we can measure ….. to measure rate

A

changes in the electrical conductivity of the reaction

41
Q

why does the boltsman curve start at the origin

A

because no molecules have zero energy

42
Q

what does the total area under the curve in the boltsman distribution represent

A

the total number of molecules

43
Q

what does the shaded area under the curve represent

A

the number of molecules with enough energy to react if they collide

44
Q

why does the curve not meet the x axis

A

there is no maximum energy for a molecule .

45
Q

at higher temperature what happens to the curve

A

peak (most probable energy) shifts to the right and down and shaded area increases as a greater proportion of collisions will lead to a reaction

46
Q

what happens to the curve in the prescence of a catalyst

A

no effect on the distribution of energies . activation energy reduced and shifts to left

47
Q

what happens at dynamic equilibrium

A

the forward and backward reactions continue at equal rates so the concentrations of reactants and products do not change

48
Q

what is a closed system

A

a system isolated from its surroundings

49
Q

what is the position of equilibrium

A

the relative quantitites of reactants and products . indicating the extent of a reversible reaction at equilibrium

50
Q

what is le chateliers pricniple

A

when a system in dynamic equilibrium is subjected to change , the system reajusts itself to minimise the effect of the change and restore equiibrium

51
Q

if concentration of a reactant is increased what will happen

A

more products will be formed until equilibrium is reached again

52
Q

if concentration of a product is decreased what will happen

A

more reactants will react until equilibrium is reached again

53
Q

if the temp of a system is increased what will happen

A

favour endo

54
Q

what does an increase in pressure do

A

shift to side with smaller amount of gas molecules

55
Q

What is Kc affected by

A

Only by temperature

56
Q

Why is high pressure bad for high yield equations

A

Provides a safety risk

57
Q

Why are higher temperatures not ideal for industrial processes

A

Higher temperatures increase energy costs

chemistry (24 decks)

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