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IP Secondary 3 Chemistry > Chapter 5 - Rate of Reaction > Flashcards

Chapter 5 - Rate of Reaction Flashcards

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1
Q

What are some examples of slow reactions?

A
  • Rusting of iron in air
  • Fermentation
  • Decomposition
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2
Q

What are some examples of moderately fast reactions?

A
  • Baking
  • Reaction of Group I metals with water
  • Contact process to manufacture sulfuric acid
  • Haber process to manufacture ammonia
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3
Q

What are some examples of very fast reactions?

A
  • Explosion of petrol-air mixture

- Precipitation of silver chloride from aqueous sodium chloride and silver nitrate

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4
Q

How can the rate of a chemical reaction be determined?

A

By measuring any property that changes over the course of the reaction

  • amount of product formed
  • amount of reactant(s) used up
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5
Q

What are some common methods to determine the rate of a chemical reaction?

A
  • Measuring mass or volume changes when a gas is evolved
  • Absorption using a spectrometer when there is a colour change
  • Measuring pH changes when there is a change in acidity
  • Measuring electrical conductivity when there is a change in the concentration of ions
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6
Q

Graph of a property against time: The instantaneous rate at any stated point in time is given by the ________ at that time

A

gradient of the graph

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7
Q

The rate of a chemical reaction usually ________ with time as reactants are ________

A

decreases

progressively used up

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8
Q

Formula to calculate rate of reaction

A

Rate of reaction = Change in (property) / Time taken

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9
Q

What are the units for rate of reaction?

A

g/s
mol dm^-3/s
cm^3/s

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10
Q

For a chemical reaction to occur, reacting particles must…

A
  1. collide with each other

2. collide with energy that is equal to or greater than the activation energy

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11
Q

What is activation energy?

A

The minimum amount of energy needed for the particles to react

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12
Q

What are effective collisions?

A

Collisions between reacting particles with energy greater than the activation energy, that result in the formation of products

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13
Q

What are the factors affecting the rate of a chemical reaction?

A
  • Temperature of the reactants
  • Concentration of the reactants
  • Pressure of gaseous reactants
  • Particle size or surface area of reactants
  • Presence of a catalyst
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14
Q

What is the effect of temperature on the rate of reaction?

A

Increased temperature → increased rate of reaction

rise in 10°C doubles the rate of reaction

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15
Q

Explain the effect of temperature on the rate of reaction

A

Particles at higher temperature → Particles gain kinetic energy and move faster → Collisions between particles more frequent → Effective collisions more frequent → Higher speed of reaction

  • As temperature increases, the particles gain kinetic energy and move faster, resulting in more collisions per second between the reactant particles
  • A greater proportion of reactant particles also possesses the activation energy required to react with one another
  • The reactant particles collide more frequently and more energetically, hence increasing the frequency of effective collisions
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16
Q

What is the effect of concentration on the rate of reaction?

A

Increased concentration → increased rate of reaction

17
Q

Explain the effect of concentration on the rate of reaction

A

More concentrated solution → More particles occupying a given volume → Collisions between particles more frequent → Effective collisions more frequent → Higher speed of reaction

  • The higher the concentration of reactants, the more reactant particles per unit volume
  • The reactant particles collide more frequently, resulting in an increase in frequency of effective collisions
18
Q

What is the effect of pressure on the rate of reaction?

A

Increased pressure → increased rate of reaction

19
Q

Explain the effect of pressure on the rate of reaction

A

Gas at high pressure → Reacting gas particles are closer together → Collisions between particles more frequent → Effective collisions more frequent → Higher speed of reaction

  • When the pressure of a gas is increased, the number of gas particles per unit volume is increased
  • The gas particles collide more frequently, resulting in an increase in frequency of effective collisions
20
Q

What is the effect of particle size (surface area) on the rate of reaction?

A

Smaller particle size (larger surface area) → increased rate of reaction

21
Q

Explain the effect of particle size (surface area) on the rate of reaction

A

Smaller particles size → Greater surface area for reacting particles to collide into → Collisions between particles more frequent → Effective collisions more frequent → Higher speed of reaction

  • For solid reactants, only the particles on the surface can come into contact with the surrounding reactant and take part in collisions
  • When a solid is in powder form, the total surface area increases
  • The gaseous or liquid reactant particles collide more frequently with the powdered solid, resulting in an increase in frequency of effective collisions
22
Q

What is the effect of presence of catalyst on the rate of reaction?

A

Presence of catalyst → increased rate of reaction

23
Q

Explain the effect of presence of catalyst on the rate of reaction

A
  • Catalysts provide an alternative reaction path of lower activation energy
  • A greater fraction of the particles will possess sufficient energy to overcome the activation energy, so the frequency of effective collision increases
24
Q

What is a catalyst?

A

A substance that

  • increases the speed of a chemical reaction
  • remains chemically unchanged at the end of the reaction
25
Q

What are the characteristics of a catalyst?

A
  • Changes the speed but not the yield of a chemical reaction
  • Only a small amount is needed to change the speed of reaction
  • Not used up during the reaction: The same amount of catalyst is present at the beginning and at the end of the reaction
  • Physical appearance may change at the end of the reaction, but the chemical properties remain unchanged
  • Lowers the activation energy of a reaction
  • Selective in its action: Different catalysts speed up different reactions
  • Impurities can prevent it from working: The catalyst is “poisoned” or “inactivated”
26
Q

Use of iron as a catalyst in the industry

A

Manufacture of ammonia from nitrogen and hydrogen (Haber process)

27
Q

Use of platinum or rhodium as catalysts in the industry

A

Catalytic converters of car exhausts

- Catalyses the conversion of carbon monoxide and nitrogen oxide into the less polluting carbon dioxide and nitrogen

28
Q

Use of aluminium oxide or silicon dioxide as catalysts in the industry

A

Production of hydrogen in the cracking process

IP Secondary 3 Chemistry (9 decks)

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