Topic 6- Rates and Equilibrium

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Chemical reactions occur when…
Different atoms or molecules collide
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For a reaction to happen particles must have a certain amount of…
Activation energy
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To increase the rate of reaction you can…
Increase the frequency of collisions or increase the energy or particles to increase the probability of successful collisions
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Activation energy…
Breaks the old bonds and forms new ones
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The rate of reaction depends on…
The temperature of the reactants, their concentration, their surface area, whether or not a catalyst is used and pressure (if a gas is involved)
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Increasing temperature increases…
Energy and therefore, collisions
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Increasing concentration increases…
Number of collisions because their are more particles to collide
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Increasing surface area increases…
Number of collisions, breaking the substance up so there are more surfaces to react with and more reactants can collide
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Increasing pressure increases…
Collisions because particles are squashed together more and are more dense
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If a catalyst is used it lowers….
The energy amount of energy needed for a reaction, so it happens faster, but the same amount of products are made
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The two ways you can work out the rate of a chemical reaction are…
Working out how quickly the reactants are used up or how quickly the products are made
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Gas syringe required practical to measure rate involves….
Collecting the amount of gas (product) produced during the reaction:
- Reaction mixture in acid
- Gas bubbles collected in a gas syringe attached to a delivery tube in a conical flask
- This measures how fast the product is made
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Gas syringe required practical without the gas syringe involves…
- Reaction mixture in acid
- Gas bubbles travel up delivery tube in conical flask
- Water filled measuring cylinder with clamp upside down in a water trough
- Gas collected in measuring cylinder, causing the water to displace
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Change in mass indicates….
The product has turned into a gas
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Measuring the formation of precipitation required practical involves…
- Conical flask with a mixture of hydrochloride acid and sodium thiosulfate
- They are both aqueous and create a solid
- Piece of paper with cross drawn on it underneath
- You will no longer be able to see the cross once it has reacted
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You should use the gas syringe method when….
You make a gas
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You should use the change in mass method when….
You start with a solid (or liquid or aqueous, but not as effective) and end with a gas
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You should use the formation of precipitation method when….
You start with two aqueous and end with a solid
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Why does the mass decrease when a solid reacts into a gas….
The gas made (refer to the equation) escapes into the atmosphere and therefore the mass is decreased
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The steeper the lime on the graph…
The faster the rate of reaction
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Over time the line on the graph becomes less steep because…
The reactants are used up
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Rate of reaction can be calculated by dividing…
The amount of reactant used of amount of product formed / time
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An exothermic reaction…
Transfers energy to the surrounding and this is shown by a rise in temperature
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An endothermic reaction…
Takes energy in from the surroundings and this is shown by a fall in temperature
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To calculate the mean reaction rate using a graph you divide…
The change in y by the change in x (for the whole graph or a section of it)
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To calculate the reaction rate for a particular point you should…
Draw a tangent meeting the point at which you want to know the rate, ensuring to adjust the ruler so the space between the ruler and the curve is equal on both sides of the point. Then pick two points on the tangent line and use them to calculate the grad
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Reversible reactions will reach…
Equilibrium
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If a reaction looks like this:
A + B ⇌ C + D
What does this mean?
The products (C and D) can react to form the reactants (A and B) again
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As the reactants react in a reversible reaction, what happens?
Their concentrations fall so the forward reaction will slow down
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As more and more products are made in a reversible reaction, what happens?
Their concentrations rise so the backward reaction will speed up
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At what point does a reversible reaction reach equilibrium?
When after a while the forward reaction begins going at exactly the same rate as the backward one
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What happens to a reversible reaction when it reaches equilibrium?
Both reactions still happen, but there’s no overall effect (dynamic equilibrium). The concentrations of reactants and products have reached a balance and won’t change. The rate of reaction on either side is the same.
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Equilibrium can only be reached if the reversible reaction takes place in…
A closed system
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A closed system means…
None of the reactants or products can escape and nothing else can get in
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In a reversible reaction, both the forward and reverse reaction are happening…
At the same time
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Certain conditions can cause a reversible reaction to…
Be more favourable to one reaction than the other, making it happen faster
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If the equilibrium lies to the right…
The concentration of the products is greater than that of reactants; and vice-versa
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The position of equilibrium depends on three conditions…
The temperature, the pressure (only with gases) and the concentration of the reactants and products; as well as the reaction itself
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If a reaction is endothermic in one direction it will be…
Exothermic in the other
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The energy transferred from the surroundings by the endothermic reaction in a reversible reaction is…
Equal to the energy transferred to the surroundings during the exothermic reaction
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An example of a reversible reaction with both endothermic and exothermic reactions is…
Thermal decomposition
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Anhydrous means…
Without water
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Hydrated means…
With water
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Thermal decomposition works by…
1 - Heat blue hydrated copper (II) sulfate crystals, which drives the watt off and leaves a white anhydrous copper (II) sulfate powder. This is endothermic.
2 - Add a couple of drops of water to the white powder and you get the blue crystals back again. T
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Thermal decomposition equation is…
Hydrated copper sulfate ⇌ Anhydrous copper sulfate + water
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If you change something in a reversible reaction…
The system will respond to undo the change
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Le Chatelier’s Principle is the idea that…
If you change the conditions of a reversible reaction at equilibrium, the system will try and counteract the change
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If you decrease the temperature at an equilibrium…
The equilibrium will move in the exothermic direction to produce more heat, so the exothermic reaction will produce more products
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If you increase the temperature at an equilibrium…
The equilibrium will move in the endothermic direction to try and decrease it, so the endothermic reaction will produce more products
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If you increase the pressure at an equilibrium…
The equilibrium tries to reduce it by moving in the direction where there are fewer molecules of gas
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If you decrease the pressure at an equilibrium…
The equilibrium tries to increase it by moving in the direction where there are more molecules of gas
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You can work out which side of a reversible reaction has more molecules of gas by…
Using the balanced symbol equation
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If you change the concentration of any of the reactants or products at an equilibrium, the system will…
No longer be at equilibrium and so the system responds by bringing itself back to equilibrium again
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If you increase the concentration of the reactants the system…
Tries to decrease it by making more products and vice-versa
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If you decrease the concentration of products the system…
Tries to increase it again by reducing the amount of reactants and vice-versa
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Other cards in this set

Card 2

Front

For a reaction to happen particles must have a certain amount of…

Back

Activation energy

Card 3

Front

To increase the rate of reaction you can…

Back

Preview of the front of card 3

Card 4

Front

Activation energy…

Back

Preview of the front of card 4

Card 5

Front

The rate of reaction depends on…

Back

Preview of the front of card 5
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