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A Level Chemistry OCR > Ch10 Rates of Reaction and Equilibrium > Flashcards

Ch10 Rates of Reaction and Equilibrium Flashcards

1
Q

What is the definition of rate of reaction?

A

ROR = change in concn of a reactant or a product in a given time.

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2
Q

What is the equation for Rate?

A

Rate = change in concn / time

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3
Q

What are the units for rate?

A

mol dm-3 s-1

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4
Q

What is collision theory?

A
  1. Particles must collide before a reaction can take place.
  2. Not all collisions lead to a reaction
  3. Reactants must possess at least a minimum amount of energy (= activation energy)
  4. Partciles must approach each other in a certain relative way (= steric effect)
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5
Q

What factors are required to increase the ROR?

A
  1. More FREQUENT collisions - increased particle speed, have more particles present
  2. More SUCCESSFUL collions - give particles have more energy, lower activation energy
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6
Q

What methods increase the rate?

A
  • Increase the SA of solids
  • Increase temp
  • Shine light (radical reactions)
  • Add a catalyst
  • Increase pressure of any gas
  • Increase the conc of reactants
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7
Q

How does increasing SA increase ROR?

A
  • Increasing SA increases chance of collision because more particles are exposed
  • Powdered solids react quicker than larger lumps
  • Catalysts are finely divided for this reason
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8
Q

How does increasing the concentration increase ROR?

A
  • Increasing conc = more frequent collisions = increased ROR

Increasing the conc of some reactants have greater effects than others.

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9
Q

How does increasing pressure increase ROR?

A
  • Increasing pressure forces gas particles closer together in a given volume
  • This increases the frequency of collisions, so ROR increases.
  • Increasing the pressure could have an affect on the position of equilibrium and therefore the yield.
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10
Q

radical reactions

How does shining light affect ROR?

A
  • shining a suitable light source onto reactants increases ROR
  • light (often UV) provides energy to break bonds and initiate reactions
  • the greater the intensity of light, the greater the effect
  • e.g. radical reactions
  • Initiation, propogation, termination
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11
Q

How does increasing temp increase ROR?

A
  • Increasing temp increases ROR
  • As particles get more energy so they can overcome the energy barrier
  • particles speeds up, also, increases the frequency of collisions.
  • Only the reactants with energy equal to or greater than Ea (Activation Energy) will react.

Look at energy profile diagrams

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12
Q

How does adding a catalyst affect the ROR?

A
  • Catalysts provide an alternative reaction pathway with lower Ea.
  • A lower Ea = more particles have sufficient energy to overcome energy barrier + react
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13
Q

What is the definition of a catalyst?

A

A catalyst lowers Ea without being chemically changed/used up at the end of a reaction.

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14
Q

Why are catalysts useful in industry?

A
  • Catalysts do not affect the position of equilibirum, therefore do not affect yield in an equilibrium system where an increase in temp = lower yield. (e.g. Haber + Contact)
  • They are safer and cheaper to use, as it means less energy is required to help reactants reach Ea.
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15
Q

What are the two types of Catalysts?

A
  • Homogenous Catalyst: same physical state/phase as reactants
  • Heterogenous Catalyst: different physical state/phase as reactants.
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16
Q

What is a limitation of using catalyst?

A

A catalyst gets affected by impurities in a chemical reaction and stops working.

17
Q

Draw a Boltzmann Distribution graph:

A
18
Q

Draw a Boltzmann Distribution graph with a curve for a higher temperature:

A
19
Q

Using a boltzmann distribution curve, explain why increasing temp increases ROR

A
20
Q

Using a boltzmann distribution curve, explain why using a catalyst increases ROR:

A
21
Q

Define: a dynamic equilibrium:

A

A dynamic equilibrium is an equilibrium that exists in a closed system, when rate of forward reaction is equal to the rate of the reverse reactions, and the concentrations of reactants and products does not change.

22
Q

What are the conditions needed for a system to reach a dynamic equilibrium?

A
  1. Rate of forward reaction equal to rate of reverse reaction
  2. Concentrations of reactants + products do not change
  3. A dynamic equilibrium occurs in a closed system
23
Q

What does Le Chatelier’s Principle state:

A

When reaction has reached dynamic equilibrium and a change occurs, (change in conc, pressure, temp) the position of equilibrium will move to counteract change and restore equilibrium.

24
Q

How does changing concentration effect the equilibrium?

A
  • If equilibrium lies to the right; increase in conc of reactants decreases conc of products.
  • If equilibrium lies to the left; decrease in conc of reactants increases conc of products.

If more products are formed, equilibrium lies to right
If more reactants are formed, equilirbium lies to left.

25
Q

How does changing temp effect equilibrium?

A
  • Depends on if +ΔH or -ΔH
  • Increase in temp shifts position in endothermic direction (+ΔH)
  • Decrease in temp shifts position in exothermic direction (-ΔH)
26
Q

How does changing the pressure of gases effect the equilibrium?

A
  • Only works if more moles of gaseous molecules on one sude than the other.
  • Increase in pressure of system shifts position of equilibrium to side with fewer moles of gas.
  • Decrease in pressure shifts position of equilibrium to side with more moles of gas.
27
Q

How does a catalyst effect the position of equilibrium?

A

Catalyst does not change position of equlibrium; it speeds up rate of forward + reverse reaction EQUALLY.

28
Q

What is the expression for Kc?

A
29
Q

What do these values of Kc tell us about the equilibrium?
* Kc = 1
* Kc > 1
* Kc < 1

A
  • Kc = 1 : position of equilibrium halfway between reactants + products
  • Kc > 1 : position of equilibrium towards products
  • Kc < 1 : position of equilibrium towards reactants

A Level Chemistry OCR (27 decks)

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