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chemistry > C10 Reaction rates and equilibrium > Flashcards

C10 Reaction rates and equilibrium Flashcards

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1
Q

Formula for rate of reaction

A

rate = change in concentration / time
( mol/dm^3/s )

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2
Q

What is the rate of a reaction?

A

Change in concentration of a reactant/product in a given time

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3
Q

Describe a concentration-time graph

A

Rate of reaction fastest as each reactant highest in concentration

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4
Q

How can you change the rate of a chemical reaction?

A

-Concentration/pressure
-Temperature
-Catalyst
-SA of reactants

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5
Q

What’s collision theory?

A

Two reacting particles must collide in the correct orientation, with sufficient energy (to overcome activation energy) for a reaction to occur

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6
Q

What is an effective collision?

A

Collision leading to a chemical reaction

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7
Q

Affect of increasing the concentration on rate of reaction?

A

-When conc of reactant inc, rate inc
-Inc number of particles in same volume
-Particles closer together so collide more freq
-More effective collisions

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8
Q

How does increasing pressure of gas affect rate of reaction?

A

-Rate inc
-Conc of gas molecules inc as same number of gas molecules occupy smaller volume
-Closer together, more freq collisions, more effective collisions

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9
Q

How can you follow the progress of a reaction?

A

-Monitor removal of a reactant (dec in conc)
-Monitor formation of a product (inc in conc)

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10
Q

How can you determine rate of a reaction that produces gases?

A

-Monitor volume of gas produced at regular time intervals (using gas collection)
-Monitor loss of mass of reactants using balance

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11
Q

What is a catalyst?

A

Substance that increases the rate of reaction without being used up
By providing alternative route of reaction with lower activation energy

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12
Q

What is an intermediate?

A

Species formed during a reaction that reacts further and isn’t present in final products

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13
Q

Features of catalyst

A

-Not used up
-May react with reactant to form an intermediate
-May provide surface for reaction to take place
-Regenerated at end of reaction

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14
Q

Draw enthalpy change profile with catalyst

A
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15
Q

What are the two types of catalyst?

A

Homogenous
Heterogenous

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16
Q

What’s a homogenous catalyst?

A

Catalyst has same physical state as reactants

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17
Q

Two examples of homogenous catalysis

A

-Esters made by a sulfuric acid catalyst (liquid)
-Ozone depletion with chlorine radicals as catalysts (gasses)

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18
Q

What’s a heterogenous catalyst?

A

Catalyst has a different physical state from the reactant

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19
Q

What is adsorption?

A

Process that occurs when a gas/liquid/solute is held to the surface of a solid
weakly bonded

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20
Q

How does a homogenous catalyst work?

A

Catalyst reacts with reactants to form an intermediate
Intermediate breaks down to give products and regenerates catalyst

21
Q

How does a heterogenous catalyst work?

A

Reactant molecules adsorbed onto surface of catalyst, where reaction takes place
Product molecules then leave by desorption

22
Q

What’s desorption?

A

Release of an adsorbed substance from a surface

23
Q

Examples of heterogenous catalysts

A

Fe (s) - Haber process/making ammonia
Pt (s) / Rh (s) - reforming
Ni (s) - hydrogenation of alkenes
V2O5 (s) - Contact process/making SO3

24
Q

How can catalysts improve sustainability?

A

-Inc rate of reaction by lowering energy requirements
-Reduces temperature and energy req

25
Q

Economic importance of catalysts

A

If a process requires less energy, costs of fuel and electricity can be cut down
Inc profitability

26
Q

What is the Boltzmann distribution?

A

Spread of molecular energies

27
Q

What does Ea represent

A

Activation energy (small proportion, area shaded under graph on right)

28
Q

What are features of the Boltzmann distribution?

A

-No molecules have zero energy (starts at origin)
-Area under curve is equal to total number of molecules
-No maximum energy for molecule (curve doesn’t meet x-axis)

29
Q

Affect of temperature on Boltzmann distribution curve (graph)

A

Avg energy of molecule increases
-Peak is lower and shifted towards right
-Ea same but has greater proportion of molecules

30
Q

Affect of temperature on Boltzmann distribution curve

A

-More molecules have an energy greater or equal to the activation energy
-Greater proportion of collisions lead to reaction, inc rate of reactiom
-Collisions become fore freq

31
Q

Affect of catalyst on Boltzmann distribution curve (graph)

A

Shifts Ea to left and becomes Ec

32
Q

Affect of catalyst on Boltzmann distribution curve

A

-Greater proportion of molecules have energy greater/equal to the lower activation energy
-More molecules have effective collisions, inc rate of reaction

33
Q

What are reversible reactions?

A

Reaction that takes place in both forward and reverse directions

34
Q

What does this <=> indicate

A

Reversible reaction

35
Q

What is dynamic equilibrium?

A

Equilibrium that exists in a closed system
where rate of forward and reverse reaction is the same
and concentrations do not change

36
Q

What is a closed system?

A

System isolated from its surroundings

37
Q

What is the position of equilibrium?

A

Relative quantities of reactants and products, indicating extent of a reversible reaction at equilibrium

38
Q

What is le Chatelier’s principle?

A

When a system in dynamic equilibrium is subjected to an external change, the system readjusts itself to minimise the effect of the change and to restore equilibrium

39
Q

What will increasing concentration of reactants do?

A

-Equilibrium shifts to right, making more products

40
Q

What will increasing concentration of products do?

A

-Equilibrium shifts to left, making more reactants

41
Q

What will changing temperature do?

A

-Inc temp shifts equilibrium position in endothermic direction
-Dec temp shifts equilibrium position in exothermic direction

42
Q

If forward reaction is exothermic, what is the effect of changing temp?

A

Inc temp - position shifts to left, more reactants made
Dec temp - position shifts to right, more products made

43
Q

If forward reaction is endothermic, what is the effect of changing temp?

A

Inc temp - position shifts to right, more products made
Dec temp - position shifts to left, more reactants made

44
Q

What will increasing pressure do?

A

-Equilibrium position moves to side with fewer gaseous moles

45
Q

What effect does a catalyst have on equilibrium?

A

Does not change equilibrium position, just speeds up the rate of reaction

46
Q

What is an equilibrium constant?

A

Measure of the position of the equilibrium
-Magnitude indicates whether there are more products/reactants
(Kc)

47
Q

What is equilibrium law?

A

aA + bB <=> cC + dD

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

-[] mean conc of

48
Q

What does the value for Kc tell us

A

-Value of 1 indicates equilibrium is halfway between reactants and products
-Value>1 indicates equilibrium towards products
-Value<1 indicates equilibrium towards reactants

chemistry (21 decks)

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