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Chemistry > Rates > Flashcards

Rates Flashcards

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1
Q

Rate of reaction

A

Change of concentration over time

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2
Q

Order

A

The effect the concentration of the reactant has on the rate

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3
Q

Overall order

A

The sum (addition) of the orders with respect to each reactant.

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4
Q

Rate constant

A

A proportional constant, which multiplies with the concentration and orders to equal the rate.

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5
Q

Half-life

A

The time for half of the reactant to be used up.

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6
Q

Rate-determining step

A

The slowest step in the series of steps which make a reaction

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7
Q

Example of a rate equation

A

Rate = k [A]^m {B]^n

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8
Q

Zero order

A

When the concentration of a reactant has no effect on the rate {A]^0

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9
Q

First order

A

The rate depends on the concentration raised to the power of one, so if the concentration is tripled the rate is also tripled. [A]^1

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10
Q

Second order

A

The rate depends on the concentration raised to the power of two, so if the concentration is tripled the rate increases by a factor of 9. [A]^2

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11
Q

Determining the units of rate constant K

A

Put the units of the rate and divide it by the units of the concentration, if it is second order you divide it by the units squared

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12
Q

How to find out K

A

Divide the rate by the concentration, if it is a second order reaction you square the concentration

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13
Q

How to find out orders

A

You compare the initial rate at various concentrations and see how much the rate changes, i.e. does it double or is it squared.

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14
Q

How can you monitor rate

A

Colorimeter, mass loss, gas collected

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15
Q

Shape of a zero order concentration-time graph

A

Straight light with a negative gradient

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16
Q

Shape of a first order concentration-time graph

A

Curve down with decreasing gradient over time, less steep then second

17
Q

Shape of a second order concentration-time graph

A

Curve, gradient decreases over time, more steep then first

18
Q

Rates and half life

A

First order reactions have a constant half life

19
Q

How to calculate rate from a graph

A

Draw a tangent at a particular concentration, the gradient of the tangent is equal to the rate.

20
Q

Calculating rate constant from half life

A

K = ln2 / half life

21
Q

Zero order rate-concentration graph

A

Horizontal straight line with no gradient, y-intercept is K. Reaction rate does not change with concentration

22
Q

First order rate-concentration graph

A

Straight line that goes through the origin. Rate constant an be determined by measuring the gradient

23
Q

Second order rate-concentration graph

A

An upward curve with an increasing gradient. Rate constant can be determined by drawing a second graph of the rate against concentration squared. This results in a straight line going through the origins, the gradient equals the rate constant

24
Q

How do you if a rate mechanism and rate determining step is correct?

A

The rate equation only includes reacting species involved in the rate determining step. The orders in the rate equation match the number of species involved in the rate determining step.

25
Q

The effect of temperature on rate constant

A

As temperature increases the rate and rate constant increase in value.

26
Q

Why does increased temperature increase the rate constant

A

The Boltzman distribution is shifted to the right so more particles have an energy above the activation energy. Particles move faster and increase more frequently

27
Q

The Arrhenius equation

A 
K = Ae^-Ea/Rt
R= gas constant
T=temperature
Ea= activation energy
A = frequency factor
28
Q

Logarithmic form of the Arrhenius equation

A

ln(k) = (-Ea / RT) + ln A

29
Q

How to get values for Arrhenius equation from a graph

A

Gradient is -Ea/R

Y intercept is A

30
Q

How does increasing the concentration affect the rate of reaction

A

An increase in concentration increases the rate of reaction. An increase in concentration increases the number of particles in the same volume. The particles are closer together and collide more frequently. In a given period of time there will be more effective collisions and an increased rate of reactions.

31
Q

Effect of pressure on the rate of reaction

A

As the pressure increases the concentration of gas molecules increases as the same number of gas molecules occupy a smaller volume. The gas molecules are closer together and collide more frequently leading to more effective collisions in the same amount of time.

32
Q

How to measure reaction rate

A

You draw a tangent and calculate the gradient. The gradient is equal to the rate

33
Q

Catalyst

A

Increases the arte of reaction without being used up itself

Chemistry (24 decks)

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