Reactivity 2 Flashcards
Stoichiometry
The fixed relationship between the number of reactant particles and the number of product particles
Formula to find out the number of moles of a gas
Volume (V)/molar volume (Vm)
Molar volume definition
The volume occupied by one mole of any gas
Limiting reactant/reagent
The reactant that is in excess, i.e runs out first
Theoretical yield definition
Maximum amount of product that could be formed according to the balanced equation
Experimental yield definition
Actual amount of product obtained when the experiment is performed
Percentage yield formula
Experimental yield/theoretical yield x 100
Factors that could cause the experimental yield to be lower than the theoretical yield
- Side reactions occurring
- Decomposition of reactants and/or products
- Loss of product during purification
- Reversible chemical reactions preventing process completion
- Incomplete reaction
Factors that could cause the experimental yield to be higher than the theoretical yield
- Impurities in a product
- When a product hasn’t been fully dried
How to find atom economy (4 steps)
- Write balanced equation
- Calculate relative molar mass, and then total mass
- Calculate relative molar mass of each desired product, and then total mass of each desired product formed
- Find atom economy using atom economy formula
Atom economy formula
Total mass of desired products/total mass of products x 100
If a use for the products are found in atom economy, what is the atom economy?
100%
Units for rate of reaction
mol dm^-3 s^-1
Collision theory
Particles must collide at the right angle with sufficient energy
How does concentration increase rate of reaction?
More collisions will occur due to the greater number of particles in the acid
How does surface area increase rate of reaction?
Only the particles on the surface can collide, if it is in powdered form there is a much greater surface area; more collisions per second
How does temperature increase rate of reaction?
The particles are moving faster; there will be more collisions per second
How does a catalyst increase rate of reaction?
Bringing the reactive parts of the reactants into close contact with each other, lowering the activation energy; less energy will be needed to collide sufficiently
Formula for rate of reaction
increase in product concentration/time taken or (-)decrease in product concentration/time taken
rise over run
Is rate positive or negative
Positive
Systematic errors
Inaccurate measurements
When all measurements are higher or lower than expected values
Cannot be fixed
Random errors
Imprecise data
Occur due to limitations in measurement equipment (uncertainties), misinterpreted measurements or not enough trials.
Can be fixed by repeating measurements and averaging results
Equilibrium law
When the rate of the forward reaction is equal to that of the reverse reaction.
Formula for K
[products]/[reactants]
If it were a reverse reaction, how would K be written?
K’
What is K dependent on?
Temperature
If K is big, what happened with the reaction and concentration?
The reaction is pretty much completed and the concentration of reactants is very small.
If K is small, what happened with the reaction and concentration?
The reaction has barely taken place and the concentration of the products is very small.
If K is around one, what happened with the equilibrium?
There will be a good amount of reactants and products in the equilibrium.
Units of K
K has no units
How to find K from K’
Reciprocal
If you add a catalyst to a reaction, what happens to the equilibrium?
Nothing
If the concentration of the products is increased, what happens to the equilibrium?
Shifts to the left
If the concentration of the reactants decreases, what happens to the equilibrium?
Shifts to the left
If the concentration of the products decreases, what happens to the equilibrium?
Shifts to the right
If the concentration of the reactants increases, what happens to the equilibrium?
Shifts to the right
If the number of mols (gas) on both sides are equal, what happens to the equilibrium?
Nothing
If there are more mols on the reactant side, what happens to the equilibrium?
Shifts to the right
If there are more mols on the product side, what happens to the equilibrium?
Shifts to the left
In exothermic reactions, lowering the temperature will do what to the equilibrium?
Shift to the right
In endothermic reactions, increasing the temperature will do what to the equilibrium?
Shift to the right
In exothermic reactions, the higher the temperature gets does what to the value of K?
It decreases the higher the temperature
In endothermic reactions, the higher the temperature gets does what to the value of K?
It increases the higher the temperature
What thing changes the K value?
Temperature
Heterogenous equilibria
When one or more of the reactants are in different phases.
How to calculate theoretical yield
Use mole ratios- perhaps with figures given in the question
If asked a question to calculate something measured at STP, how do you find it?
Multiply the ‘n’ value by 22.7 (STP value)
