The maximum mass it is possible to make from a given mass of reactants
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What is the calculation for percentage yield?
percentage yield = actual yield/theoretical yield x 100
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Why may a percentage yield be below 100%?
Reactants may react in a different way than expected, reaction may not go to completion, some of the product may be lost when you separate it from the reaction mixture to purify it
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Define atom economy
A measure of how many atoms in the reactants form a desired product
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What is the equation for atom economy?
Atom economy = RFM of desired product / sum of RFM for all products x 100
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What factors should you consider when choosing a reaction pathway?
Yield of the product, atom economy of reaction, usefulness of by products, rate of reaction, equilibrium position and whether it's a reversible reaction
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Define by product
A substance formed in a reaction in addition to the desired product
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How do you convert cm^3 to dm^3?
Divide by 1000
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What equation links concentration, mass, and volume?
concentration = mass/volume
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What equation links concentration, moles, and volume?
Concentration = moles / volume
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Define concentration
The amount of substance present in a given volume
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What is a titration used for?
To find the concentration of an unknown solution
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What is the long glass tube called in a titration?
Burette
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Why should you use a single indicator in a titration?
So there is a sudden colour change and therefore producing a more accurate reading
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What are some potential errors in a titration?
The burette not being clamped vertically, eye protection not being worn
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What piece of equipment can you use to accurately measure a volume of liquid?
Volumetric Pipette
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How much of the known solution should you use in a titration?
25cm^3
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Define titre
The difference between the initial burette reading and the final burette reading
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How should you take a burette reading?
Take the reading off the bottom of the meniscus
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Define meniscus
Curved surface of liquid
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What are concordant titre results?
Within 0.1cm^3 of each other
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What volume does 1 mole of gas occupy?
24dm^3
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What equation can be used to identify gas volume?
Volume = amount in mol x 24dm^3
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Define rate of reaction
A measure of how quickly reactants are used or products are formed
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What is the calculation for rate of reaction?
Rate = amount / time taken
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How can you measure rate of reaction with gas?
Attach conical flask to gas syringe and react magnesium with HCl, measure how much hydrogen gas given off after set time
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What factors increase rate of reaction?
Catalyst, higher temperature, increased concentration, larger surface area
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Why does increasing temperature increase rate of reaction?
Particles have more kinetic energy, so move faster, so have a higher chance of successfully colliding, meaning they have a higher chance of reacting
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When will a collision not be successful?
If particles have less energy than the activation energy
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Define activation energy?
The minimum amount of energy required to start a reaction
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What relationship does reaction time have with rate of reaction?
Inversely proportional
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Why does increasing concentration increase rate of reaction?
There are more particles in a given volume, so they are closer together, meaning the chance of successful collisions are higher
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When measuring rate of reaction using magnesium ribbons, what should be controlled?
The length of the magnesium ribbon
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Why does a reaction go faster at a higher pressure?
Particles become more crowded so higher chance of successful collisons
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Why does increasing surface area increase rate of reaction?
More reactant particles are available for collisions, therefore collisions are more likely, therefore more successful collisions
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Define catalyst
A substance that speeds up the rate of chemical reaction but is unchanged itself in a reaction
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Give an example of a catalyst in biological systems?
Enzymes
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How do catalysts work?
They provide an alternative reaction pathway with a lower activation energy, so more particles can successfully collide and react
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What is a reversible reaction?
A reaction where the products can react together to form the original reactants
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What happens at equilibrium?
The concentrations of all reacting substances remain constant, forward and backward reactions still happen so it's a dynamic equilibrium
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What conditions are needed for dynamic equilibrium?
Closed system and a constant temperature
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Define dynamic equilibrium
When the rate of the forward reaction is equal to the rate of the reverse reaction and concentrations of reactants and products remain unchanged
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When will the equilibrium be on the left? (Concentration)
When the concentration of reactants is greater than the concentration of products
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What happens to the equilibrium position if pressure is increased?
Moves towards the direction of the least moles of gas
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What happens to the equilibrium position if you increase concentration of a substance?
Position moves away from that that substance
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What happens to the equilibrium position if temperature is increased?
Moves in the direction of the endothermic change
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What does the equilibrium yield depend on?
Pressure and temperature
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Define equilibrium yield?
The amount of desired product present in a reaction at equilibrium
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State Le Chatelier's principle
If a system is at equilibrium and a change is made to any of these conditions, then that system will respond to counteract the change
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What happens to the mass of a catalyst as the reaction occurs?
Remains unchanged
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Why doesn't an increase in temperature affect the yield of a product?
Higher temperature favours endothermic reaction so equilibrium shifts to left hand side
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Describe in detail an experiment on how concentration of acid affects the rate of reaction
Add 10cm^3 of sodium thiosulfate solution to a conical flask, then add 40cm^3 of water. Measure and record temperature of the solution. Place the conical flask on a piece of paper with a black cross drawn on it. Add another 10cm^3 to the flask and start a stopwatch. When the cross is no longer visible stop the stopwatch and record the time taken in a table. Repeat the experiment 5 times, using different concentrations each time. Calculate rate of reaction using volume/time.
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