Rate of Reaction summary

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Summary of all topics covered Collision Theory

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Collision Theory (using bullet points - )

-Must collide with activation energy to be successful (if not particles bounce off each other with no successful collisions so no reaction occurs)

-RATE OF REACTION depends on two things: how frequently and forcefully particles collide.

-if frequency and forcefulness are changed, RATE OF REACTION will change

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<p>Collision Theory explanations: Label A, B, and C in terms of <strong>collision theory</strong><br><br>*This is accurate for <strong>any fizzy reaction</strong></p>

Collision Theory explanations: Label A, B, and C in terms of collision theory

*This is accurate for any fizzy reaction

A: many reacting particles, very frequent collisions

B: fewer reacting particles, less frequent collisions

C: no more reacting particles as one reactant has been used up

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<p>Label A, B and C (<strong>not</strong> collision theory)<br><br>*This is accurate for <strong>any fizzy reaction</strong></p>

Label A, B and C (not collision theory)

*This is accurate for any fizzy reaction

A: Reaction fastest (steepest gradient)

B: Reaction slowing (less steep gradient)

C: Reaction stops

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Rate of Reaction definition

the change in amount of substance per second

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To find mean rate

read off graph and divide y/x

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To find mean rate using a tangent

Draw tangent, turn into triangle, divide y/x

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Gas Syringe Method definition

The gas syringe is used to collect and measure the amount of gas produced during a reaction from a conical flask.knowt flashcard image

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Gas Syringe Method Advantages

Good Resolution, Gases are not released into the room.

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Gas Syringe Method Monitoring Options

Either decide time and measure volume or decide volume and measure time or measure at intervals.

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Mass Loss method definition

MEASURES GAS: Use scales to measure how much mass is lost with conical flask and cotton wool ball (only allows gas to escape, not liquid).C6 B) Rate of Reaction – AQA Chemistry - Elevise

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Mass Loss method advantages

Excellent resolution: masses measured to the nearest 0.01g

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Mass Loss method disadvantages

Gases are released into the room

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Mass Loss method monitoring options

Either choose time and measure mass loss or choose mass loss and measure time. Or measure at regular time intervals.

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Monitoring Rate of Reactions that don’t produce gas: DEFINITION

If no gas is produced and reaction produces a precipitate or dark colour, time how long it takes for a cross on piece of paper to disappear.

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Conical Flask

knowt flashcard image

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Precipitate

A solid formed by change in solution.

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What factors affect rate

Surface Area, Concentration, Pressure, Temperature

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Repeatable

I do it lots and get the same results

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Reproducable

Others do it lots and get the same results

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In the order Concentration, Surface Area, Pressure, Temperature how do these factors effect rate?

Concentration: Higher concentration, faster rate of reaction
Surface Area: Larger surface area, faster rate of reaction.
Pressure: Increased pressure, faster rate of reaction.

Temperature: Increased temperature increases rate of reaction.

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How is pressure caused?

Gas particles colliding with container walls

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When does a reaction stop?

When one reactant has been used up so there are no more collisions.

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Independent Variable

What I change

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Dependent Variable

What I observe

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Controlled Variable

What I keep the same

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Explain, in terms of particles, why rate of reaction increases with temperature.

-Temperature increase means particles have more energy
-Particles have activation energy
-More frequent collisions

-More forceful collisions

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What does a Catalyst do?

Provides a new route for a reaction with lower activation energy so particles can collide more frequently

particles HAVE NOT got more energy!! ONLY

temperature increase can do this

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Who are the best catalysts?

Transition metals (specifically manganese oxide) and their compounds

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Advantages of using a catalyst + explanations

Reactions done at lower temperatures
-less non-renewable fossil fuels used

-less CO2 emissions, less global warming

-less SO2 emissions, less acid rain

-less NOx emissions, less acid rain

-less particulates, less global dimming and lung diseases

Sustainable

-less non-renewable sources of metal catalyst used

-less mining of metal catalyst, less habit destruction

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Disadvantages of using a catalyst + explanations

Fill up landfill sites on disposal:
-they do not decompose/rot
-can contain toxic poisons that enter environment
Eventually stop working so mining of metal catalysts:
-expensive to mine/extract
-rare metals are very expensive to mine/extract

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floating head reaction
RP: Sodium Thiosulphate-HCl Reaction
Important information

-no gas produced in this reaction so we cannot use a gas syringe or a balance to monitor it
-A yellow precipitate of sulphur is produced (S(s))
-we measure time taken for the cross to dissapear

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floating head reaction
RP: Sodium Thiosulphate-HCl Reaction
What is it used for?

Any reaction that produces a precipitate or a dark colour

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floating head reaction
RP: Sodium Thiosulphate-HCl Reaction

Variables

IV: Concentration of ‘thio’
DV: Time for cross to disappear
CV: Concentration of HCl
Volume of HCl

Total volume of ‘thio’
Constant Temperature

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floating head reaction
RP: Sodium Thiosulphate-HCl Reaction
Accuracy

To improve accuracy
-use pipette or burette to measure vol

-use light sensor connected to a data logger to measure when light intensity drops to a certain value (as precipitate forms)
-use water bath set at fixed temp to keep contents in a flask at a constant temperature

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Calcium Carbonate (marble) or Magnesium HCl reaction
Methods

-Measure gas volume with a gas syringe

-Measure mass loss using a balance

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Calcium Carbonate (marble) or Magnesium HCl reaction
Variables

IV: Concentration of HCl
DV: Time for cross to disappear
CV: Total voume of HCl
Same mass of solid
Constant room temperature

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Calcium Carbonate (marble) or Magnesium HCl reaction
Accuracy

To improve accuracy:
-use pipette or burette to measure volume

-use water bath set at fixed temp to keep contents at a constant temp.

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How to prove a Catalyst can not be used up

-weigh catalyst

-filter mix

-dry catalyst

-reweigh cat.

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Endothermic

reactants absorb heat energy from the surroundings to form products

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Exothermic

releases heat, causing the temperature of the immediate surroundings to rise

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<p>Volume/Mass Loss vs time graph</p>

Volume/Mass Loss vs time graph

Lower Concentration: Slower (less steep) and less gas produced
Halving concentration: halves volume/ mass gas produced

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Concentration mathematical link

-Rate directly proportional to concentration (rate ∝ concentration)
e.g if doubling conc doubles rate
twice as many reacting particles
twice as many frequent collisions

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Temperature mathematical link

-Rate is NOT directly proportional to temperature
-Rate approximately doubles per 10 degree rise

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More diluted solution means

Less gas produced (less steep line, finishes later)

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Change in surface area

Does not change how much gas is produced, just gives a much faster reaction

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Surface area mathematical link

-rate is directly proportional to surface area

-e.g doubling surface area doubles rate
twice as many reacting solid particles available

twice as many frequent collisions

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Pressure mathematical link

-rate directly proportional to pressure
-e.g doubling pressure doubles rate
same number of particles in half the volume
twice as many frequent collisions

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Straight line through origin

Directly proportional

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Change in temperature

Does not change amount of gas produced, just gives a faster reaction

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<p>Change in temperature graph</p>

Change in temperature graph

Not straight line through the origin:

Rate is not directly proportional to temperature
Pattern is called ‘exponential’

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‘exponential’

increase one thing by a certain amount each time (eg 10 degrees)

other ‘thing’ increases by more and more each time
(eg by 2, then 7, then 25 etc)

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The most common reactions that produce gas

Adding metal to an acid to produce H2 gas
for example:

Magnesium + Hydrochloric Acid → Magnesium Chloride + Hydrogen

Adding a carbonate to an acid to produce CO2 gas
for example:
Calcium Carbonate + Hydrochloric Acid → Calcium Chloride + Carbon Dioxide + Water

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The rate of any reaction that produces a gas

can be measured by mass loss or gas volume methods

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A successful collision means

bonds are broken in reactants

the particles separate from each other

they combine differently

new bonds form between them to make the products

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Making catalysts even better

-Powdered Catalysts: Large Surface Area, Reactions go even faster
-Nanocatalysts: Huge surface area to volume ratio (huge surface area compared to volume)

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Catalysts and rate

Hydrogen Peroxide solution (aq) breaks down very slowly. Can be sped up using a catalyst.