C5 - Monitoring And Controlling Chemical Reactions
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Describe the yield of a reaction
The yield of a reaction is the mass of the desired products which is made
Describe the theoretical yield of a reaction
The theoretical yield is the maximum possible mass of desired products you can make from a given mass of reactants
Describe the actual yield of a reaction
The actual yield is the mass of products you actually make
How do you calculate percentage yield?
Percentage yield = Actual yield / Theoretical yield x 100
What factors affect percentage yield?
• Reactants reacting in an unexpected way • Reaction not going to completion • Losing products when separating or moving the substance
What is atom economy?
Atom economy is a measure of how many atoms in the products make up the desired product
How do you calculate atom economy?
Atom Economy = Mr of desired products / Mr of all products x 100
What factors should be considered when making a substance?
• Cost • Rate of reaction • Equilibrium
What are by products?
By products are the other products formed in a reaction that aren’t the desired products
Important conversions for concentration:
1dm3 = 1L 1cm3 = 1ml cm3 /1000 = dm3 dm3 x 1000 = cm3
Equation for concentration:
Concentration = Amount in moles / Volume
What are the units for concentration?
g/dm3 mol/dm3
How do you calculate a new concentration from a given concentration and volume?
To calculate the new concentration: C1V1 = C2V2 Worked example: 20cm3 of 2mol/dm3 HCl was added to 80cm3 of water - what is the new concentration? • First assign the values for C1, V1, C2, V2 - C1 = 2mol/dm3 V1 = 0.020 dm3 C2 = ? V2 = 0.1dm3 • Substitute values and rearrange - 2 x 0.02 = C2 x 0.1 C2 = 2 x 0.02 / 0.1 = 0.4 mol/dm3
What is a titration?
A titration is a method used to find an unknown concentration
Define a ‘titre’
Volume of solution added from a burette during a titration
What are concordant results?
Titres which are within 0.1cm3 of each other
What is molar volume?
1 mol of any substance in the gas state occupies the same volume at the same temperature and pressure At room temp and pressure, the molar volume is 24dm3
What equation links gaseous moles and molar volume?
Amount (mol) = volume (dm3) / 24
Define ‘rate of reaction’
How quickly reactants are used up or products are formed
How do you calculate rate of reaction?
Rate of reaction = Amount of products produced / time Rate of reaction = Amount of reactants used / time
What is ‘collision theory’?
In order for two particles to react with each other, two things need to happen: • Reacting particles need to collide • They need to have enough energy (more than activation energy) If these two things happen: a successful collision will occur
Something will increase the rate of reaction if it:
• Increases the number of collisions • Increases the percentage of successful collisions
When the temperature of a reaction is increased:
• The number of collisions increase as the particles are moving more quickly • The percentage of collisions which are successful increases because all the particles have more energy This results in an increase in rate of reaction
How does an increased concentration affect rate of reaction?
Increasing concentration increases the reaction rate because the particles have become more crowded which increases the number of collisions