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Z/ HIGHER Chemistry > Unit 1: Chapter 1 - Reaction Rates > Flashcards

Unit 1: Chapter 1 - Reaction Rates Flashcards

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1
Q

What does how steep the reaction curve tell us about the reaction rate?

A

How fast the reaction is proceeding.

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2
Q

What is the equation for reaction rate?

A

reaction rate = change in quantity/change in time

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3
Q

What is the equation for reaction rate when only given the time?

A

Reaction rate = 1/t

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4
Q

When do reactions take place?

A

When there are SUCCESSFUL COLLISIONS between reactants.

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5
Q

How can you speed up a reaction?

A
  • Decreasing the PARTICLE SIZE of any solid. (Increased surface area = increase in the probability of SUCCESSFUL COLLISIONS).
  • Increasing the CONCENTRATION of a solution. (Increasing the NUMBER OF PARTICLES = increase in the probability of SUCCESSFUL COLLISIONS.)

• Increasing the TEMPERATURE of the reaction.
(Increases the amount of energy and the speed of particles = increase in the probability of SUCCESSFUL COLLISIONS.)

• Using a Catalyst. (Increases the probability of SUCCESSFUL COLLISIONS.) (Is not used up and can be used again)

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6
Q

What do all molecules and atoms have?

A

Kinetic energy

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7
Q

What does collision theory state must happen for a reaction to take place?

A

Collision theory states that in order for a reaction to take place the particles in the reactants must collide.

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8
Q

What molecules will collide successfully in collision theory?

A
  • Molecules with sufficient energy will collide successfully and will react i.e. molecules with more energy than the activation energy.
  • Even if there are sufficient energy the molecules have to have the correct collision geometry too.
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9
Q

How can sufficient energy for successful collisions be achieved?

A

With an increase in temperature the molecules will gain kinetic energy, and more molecules will have the required energy to collide successfully and to react.

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10
Q

What is the activation energy?

A

The point where particles will have enough kinetic energy to make a successful collision.
or
The activation energy is the minimum energy required by colliding particles to form an activated complex.

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11
Q

In exothermic reactions what is the ΔH?

A

Negative

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12
Q

In endothermic reactions what is the ΔH?

A

positive

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13
Q

What is enthalpy?

A

A measure of the change in potential energy between the reactants and the products of a reaction.

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14
Q

What changes enthalpy?

A

ΔH

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15
Q

What is not dependent on the change in enthalpy?

A

The rate of reaction.

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16
Q

Unless stated on the graph what is enthalpy measured in?

A

kJmol-1

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17
Q

What is an exothermic reaction?

A

An exothermic reaction involves the reaction RELEASING energy to the surroundings, usually in the form of heat.

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18
Q

What is an endothermic reaction?

A

An endothermic reaction ABSORBS energy (usually in the form of heat) form the surroundings.

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19
Q

What are examples of Exothermic reactions?

A
  • Combustion - hydrocarbons and carbon compounds.
  • Neutralisation - Using alkalis and reactive metals.
  • Displacement - Reactive metal displacing a less reactive metal.
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20
Q

What are examples of endothermic reactions?

A
  • Dissolving certain salts in water, e.g. ammonium nitrate or potassium nitrate.
  • Neutralising ethanoic acid or sodium hydrogecarbonate.
  • Making a fuel called ‘ water gas ‘ by reacting steam with hot coke.
21
Q

What does the activation energy act as?

A

The activation energy acts like a sort of barrier which has to be overcome to allow a reaction to proceed.

22
Q

What does ‘ whether a reaction is fast or slow ‘ depend on?

A

The height of the activation barrier.

23
Q

What does a catalyst provide?

A

A catalyst provides an alternative reaction pathway with a lower activation energy but does not have an effect on ΔH.

24
Q

Is the reaction rate slower for a reaction with a higher activation energy?

A

Yes

25
Q

Is the reaction rate slower for a reaction with a lower activation energy?

A

No it is faster.

26
Q

Does the activation energy have any relationship to the change in enthalpy?

A

NO

27
Q

In an exothermic reaction Is the potential energy of the reactants higher than the potential energy of the products and why is this?

A

Yes as the reaction is releasing/losing energy to the surroundings.

28
Q

In an endothermic reaction Is the potential energy of the reactants higher than the potential energy of the products and why is this?

A

No, the potential energy of the products is higher than the potential energy of the products as the reaction absorbs energy from the surroundings.

29
Q

What does a higher barrier from the reactant to the activated complex mean for the complex?

A

The complex is more unstable the higher the barrier is from the reactant.

30
Q

What is the activated complex?

A

As the reaction proceeds, the reactants reach an intermediate stage at the top of the energy barrier. At this point the reactants are called the activated complex.
or
The activated complex is an unstable arrangement of atoms formed at the maximum of the potential energy barrier, during a reaction.

31
Q

How can an activated complex become more stable?

A

By losing energy by:

  • Breaking up and returning to individual reactants
  • Completing the reaction and becoming products.
32
Q

What is the activation energy measured in?

A

kJmol-1

33
Q

What happens in regards to activation energy when a catalyst is added?

A

The activation energy decreases.

34
Q

What does a catalyst provide the molecules with and how does this affect the reaction?

A

By adding a catalyst you the molecules are provided with an alternative reaction pathway, which lowers the energy required to allow the reaction to occur. This also allows more of the reactants to overcome the energy barrier and increase the reaction rate.

35
Q

How does industry use catalysts?

A

In industry, companies can use catalysts to save energy as lower temperatures can be used which results in lower costs and a saving of money.

36
Q

What do catalysts do to a reaction?

A

Catalysts speed up the rate of reaction and are not used up during the reaction and can be recovered after the reaction and used again.

37
Q

What are the two types of catalysts?

A

Heterogeneous and homogeneous.

38
Q

What do homogeneous catalysts do?

A

Speed up reactions where the reactant is in the same state as the catalyst, i.e liquid reactants and a liquid catalyst.

39
Q

What do hetrogeneous catalysts do?

A

Speed up reactions where the reactant and the catalyst are in different states, i.e. liquid reactants and a solid catalyst.

40
Q

How do heterogeneous catalysts work?

A
  • Adsorption - Molecules of one of the reactants form bonds with the catalyst. This weakens the bonds within the molecule.
  • A collision is made with another reactant molecule, bonding with the molecule attached to the site.
  • Reaction - the molecules react on the catalyst surface. The angle of collision is more favourable as one of the molecules id fixed.
  • Desorption - The product molecules leave, leaving behind a vacant site.
41
Q

What is adsorption in catalysts?

A

Occurs when molecules attach themselves to the catalyst,

42
Q

What is desorption in catalysts?

A

Occurs when the molecules leave the surface.

43
Q

What is catalyst poisoning?

A

Where IMPURITIES PERMANENTLY BLOCK the active site decreasing the efficiency of the catalyst.

44
Q

How do catalysts actually speed up the reaction?

A

As the molecules are held in a fixed position by the catalyst it is easier for the molecules to collide/there is a higher chance of the molecules colliding.

45
Q

How can you spot if a catalyst has been used in a reaction?

A

one of the elements/molecules/compounds has not been used up.

46
Q

Why do boiling points increase going down group 7?

A

Intermolecular forces/bonds increase going down the group. LDFs are the forces (broken)between the molecules.The more electrons the stronger the
LDFs.

47
Q

Collision theory can be used to explain reaction rates. Collision theory states that for two molecules to react, they must first collide with one another. State a condition
necessary for the collisions to result in the formation of products?

A

Favourable collision geometry, particles must collide with a greater than or equal to the activation energy.

48
Q

How can you alter/change the concentration?

A

By diluting with water and keeping the total volume the same.

49
Q

A collision involving molecules with the required energy of activation may not result in a reaction. State a reason for this?

A

The orientation/geometry is incorrect.
or
The activated complex breaks up to reform the reactants.

Z/ HIGHER Chemistry (25 decks)

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