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chem class > 3.1.5 Kinetics > Flashcards

3.1.5 Kinetics Flashcards

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1
Q

What is a reaction rate?

A

Change in concentration (or amount) of reactant or product over time

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2
Q

State the formula for a rate of reaction

A
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3
Q

Name the 2 conditions needed for particles to react with one another when they collide

A
  • Collide in right direction
    • Need to be facing each other in right way
  • Collide with certain minimum amount of kinetic energy
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4
Q

What is meant by activation energy?

A

Minimum (amount of kinetic) energy needed for a reaction to occur

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5
Q

Why do particles need a minimum amount of kinetic energy for them to react?

A

Need to have this much energy to break their bonds & start reaction

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6
Q

Molecules in gas don’t all have the…

A

same amount of energy

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7
Q

What does a Maxwell-Boltzmann distribution show?

A

Number of molecules in a gas with different kinetic energies

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8
Q

Draw a Maxwell–Boltzmann distribution

A
  • (y axis) %/fraction of particles/molecules/atoms
  • (x axis) energy
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9
Q

Maxwell–Boltzmann Distribution

What does the peak of the curve represent?

A
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10
Q

Maxwell–Boltzmann Distribution

Where is the mean (average) energy of all molecules on the curve? Label it on your curve.

A
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11
Q

Maxwell–Boltzmann Distribution

At what speed are most molecules moving at?

A
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12
Q

Maxwell–Boltzmann Distribution

Shade the area where there’s molecules that can react

A
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13
Q

What is the area under a Maxwell–Boltzmann distribution curve equal to?

A

Total number of molecules

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14
Q

Why does the Maxwell–Boltzmann distribution curve start at (0,0)?

A

Because no molecules have 0 energy

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15
Q

Describe the effect of temperature on reaction rate

A
  • ↑ temp of reaction = particles have more kinetic energy ∴ move faster
  • Greater proportion of molecules E ≥ Ea & able to react (have at least activation energy)
  • More frequent successful collisions in given time
    • Another reason why ↑ temp = reaction faster
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16
Q

Describe and illustrate the effect of an increase in temperature on Maxwell–Boltzmann distribution curve

A

Changes shape of Maxwell–Boltzmann distribution curve → shifts to the right

17
Q

Why does a small increase in temperature create a large increase in reaction rate? (2)

A
  • Many more molcules have E ≥ Ea (energy greater than the activation energy)
  • Far more successful collisions per second
18
Q

Describe the effect of concentration on reaction rates

A
  • ↑ concentration of reactants in solution = particles will be closer together
  • Closer = collide more often
  • Collisions occurring more frequently = more chances to react
  • Explains why ↑ concentration = ↑ reaction rate
19
Q

Describe the effect of pressure on reaction rates

A
  • Gas particles closer together
  • ↑ collsion frequencies = reaction rate ↑
20
Q

What is a catalyst?

A
  • Substance that increases the rate of reaction by providing an alternative reaction pathway with lower activation energy
  • Catalyst is chemically unchanged by end of the reaction
21
Q

Catalysts take part in reactions but…

A

are remade at end

22
Q

Draw a Maxwell–Boltzmann distribution showing the effect of a catalyst work

A
23
Q

Describe how you can measure reaction rates

A

Measure how fast reactants are used up or how fast products are formed

24
Q

Name 3 ways to measure reaction rates

A
  1. Timing how long a precipitate takes to form
  2. Measuring a decrease in mass
  3. Measuring the volume of gas given off
25
Q

Measuring reaction rates

Describe “measuring a decrease in mass”

A
  1. When one or more products is gas = measure rate of formation using mass balance
  2. As gas given off, mass of reaction mixture decreases
  3. Method is accurate & easy to do
    • Usually done in fume cupboard
26
Q

Measuring reaction rates

Describe “measuring the volume of gas given off”

A
  1. Uses gas syringe to measure volume of gas being produced
  2. Use it when 1 or more products is gas
  3. Method is accurate

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