Rates of reaction Flashcards
Define exothermic reactions.
transfers energy to surroundings, so temp rises
Define endothermic reactions.
Takes in energy from surroundings, so temp falls.
What is the activation energy?
The minimum amount of energy needed required for particles to collide and react.
Where is activation energy found on exo/endo graphs?
Line from curve to reactants.
In exo graphs, are reactants higher or lower energy than products?
Higher
In endo graphs, are reactants higher or lower energy than products?
Lower
Explain the differences between endo and exo graphs.
Reactants>products, exo
Product>reactants, endo
In exo, energy is released rather than absorbed (reactants to products)
RQ4: Give the method of finding temperature changes.
-measure 30cm3 of HCl acid into polystyrene cup and measure temp.
-measure 5cm3 of NaOH into polystyrene cup.
-place lid with thermometer
-repeat 3 times and increase by 5cm3 each time
What is bond energy?
Amount of energy required to break one mole of a particular covalent bond
How do we know if a reaction is endothermic or exothermic using bond energies?
Reactant>product(+), Endo
Products>reactants(-), Exo
What is meant by ‘rate of reaction’?
Speed at which reactants turn into products
What are the 2 formulas to find the average rate of reaction?
Amount of reactants used up/time taken
Amount of products formed/ time taken
Why is a mean calculated for rates of reaction?
In reality, product formed is fast then slows down
Explain the collision theory.
For particles to react, they need to have sufficient energy and correct orientation to achieve activation energy
What are the 2 things that can increase a rate of reaction?
1- Amount of energy
2- Frequency of collisions
What are the factors that cause either an increase in energy or frequency of collisions?
and explain them
-Temperature, more energy = more collisions
-Pressure, more likely to collide
-Surface area of reactant, powder has more area over which collisions occur
-Catalyst, speeds up reaction by lowering activation energy
RP5: Effect of concentration on rate of reaction in liquids
Measure 50cm3 of sodium thiosulfate solution, measure 5cm3 HCl into a measuring cylinder, add to flask on top of paper with a cross, add acid into flask + start the stopwatch, stop when cross not seen, repeat using different concentrations of sodium thiosulfate solution.
What causes the reaction of sodium thiosulfate and HCl to become cloudy
Sulfur as product
RP5: Effect of concentration on rate of reaction in gases
Measure 50 cm3 dilute HCl into a flask, add Mg ribbon into flask and connect it to the gas collection equipment (syringe), start stopwatch and record the volume of gas every 10 seconds, When reaction completes, repeat using higher conc of HCl
What is the problem with using crosses and cloudiness of reaction to measure rate of reaction?
Eyesight, people may have different levels
For particles to react successfully, they must…
1- collide
2- reach activation energy
3- collide in correct orientation
What is meant by a reversible reaction?
Reactants can form products, and products can form reactants
If a reversible reaction is exothermic in one direction, it is..
endothermic in the other direction
Explain how equilibrium is achieved.
When a reaction is being carried out, the forward reaction will be faster than the backwards (since there are more reactants than products), then the backwards reaction speeds up and the rate will equal eachother
Define equilibrium
When the rate of forwards and backwards reactions are equal (doesn’t mean amount of reactants and products are equal)
If equilibrium is to the right, what does it mean?
When the reaction is at equilibrium but there are more products
What is Le Chatelier’s principal?
If a change is made to an equilibrium in a reversible reaction, it will shift to oppose this change.
If we increase the temperature of the reactants, the equilibrium will shift to…
The left to form more reactants
If we increase the concentration, the equilibrium will shift to the…
the side with less molecules (concentration) so the right
