C8 - Rates and Equilibrium Flashcards
What are 2 general ways to calculate the rate of a reaction?
-mass of reactant used up in a period of time
-mass of product formed in a period of time
How can mass loss be used as a method to investigate rate of reaction?
-placing reaction container on mass balance and measuring mass decrease due to gas produced
-cover flask container with cotton wool to stop liquid spitting out (still allows gas to escape)
Name 5 factors that affect the rate of a chemical reaction:
-conc. of reactants in solution
-pressure of reacting gases
-SA of solid reactants
-temperature
-presence of catalysts
How does increasing SA affect rate of reaction?
-higher number of particles available to collide with
-more frequent collisions
-more frequent successful collisions, increasing RoR
How does increasing the concentration of reactants in solution affect rate of reaction?
-particles are closer together per unit same volume
-available to collide more
-more frequent collisions
-more frequent successful collisions, increasing RoR
How does increasing the pressure of reacting gases affect rate of reaction?
-particles are closer together per unit volume
-available to collide more
-more frequent collisions
-more frequent successful collisions, increasing RoR
How does increasing the temperature affect rate of reaction?
-higher average particle speeds due to increased thermal energy
-more particles with energy above activation energy
-more frequent collisions
-more frequent successful collisions, increasing RoR
How does introducing a catalyst affect rate of reaction?
-lowers activation energy
-each particle needs less energy for a successful collision
-more frequent collisions
-more frequent successful collisions, increasing RoR
What is collision theory, and what does it explain?
-a theory that says chemical reactions can only occur when reacting particles collide with each other and with sufficient energy (activation energy)
-explains how various factors affect RoR
This can be applied to C7 (energy changes) too
What is activation energy?
the minimum amount of energy needed for a successful collision
What is a catalyst, and how do they work?
-a substance that increases the rate of chemical reaction but isn’t used up in the reaction itself
-they do so by providing an alternate pathway for the reaction to occur that has a lower activation energy
What is a reversible reaction?
a type of chemical reaction where, under certain conditions, the products formed can react again to reform the original reactants
Give the word equation for the ammonium chloride reversible reaction:
Describe the energy changes in a reversible reaction:
if exothermic in one direction it will be endothermic in the other, and the same amount of energy is transferred either way
If it didn’t do that, it would mean that energy would is created/destroyed
Give the word equation for the copper sulfate reversible reaction:
What is dynamic equilibrium and when does it occur?
-when the forwards and reverse reactions occur at exactly the same rate, so the masses of the products and reactants remain constant (but not necessarily equal)
-only happens during a reversible reaction in a container where no matter enters/leaves (a closed system)
What is Le Chatelier’s principle?
whenever a change in conditions (eg conc., pressure, temp.) is introduced to a system at equilibrium, the position of equilibrium shifts to counteract the change
What does it mean for the equilibrium to lie to one side?
eg: if eq. lies to left, there are more reactants than products
This could mean a higher mass, concentration, or volume depending on what the reactants are (like solids, solutions, etc)
What is the effect on the position of equilibrium if you change the concentration of the reactants?
-increasing reactants is counteracted upon by more forming products until eq reached (lies to the right)
-decreasing reactants is counteracted by products reforming the reactants (eq. lies to the left)
More thiocyanate ions are added to a solution at equilibrium containing the ions below - explain what happens after:
SCN⁻ is thiocyanate
-position of equilibrium shifts to the right to increase the concentration of the product
-this counteracts the initial increase in SCN⁻ ions, as more of them react to form the product, which then decreases the concentration of SCN⁻ ions
Where does the equilibrium lie if you change the concentration of the products?
-increasing products gets counteracted by more reforming the reactants until eq reached (lies to left)
-decreasing products is counteracted by more reactants forming the products until eq reached (lies to right)
What does the energy symbol mean next to a chemical equation?
-overall energy change of the substances used in the forward reaction
-if negative, forward reaction is exothermic (products lose energy)
-if positive, forward reaction is endothermic (products gain energy)
What happens if the temperature is changed in a reversible reaction?
-if temperature increased, reaction takes in more energy to counteract the change and the eq moves in the direction of the endothermic reaction
-if temperature decreased, reaction releases more energy to counteract the change and the eq moves in the direction of the exothermic reaction
What happens if the pressure is changed in a reversible reaction?
ONLY WORKS WITH GASES
-if pressure increased, the eq will move to the side where there are fewer moles of gas, as less particles means lower pressure
-if pressure decreased, the eq will move to the side with more moles of gas, as more particles will increase the pressure
How will adding a catalyst affect the eq. in a reversible reaction?
-no effect
(however it will bring the reactants to the eq. faster)
If both sides of the equation have the same moles of gas, how will the eq. shift if pressure is changed (in reacting gases)?
-no change
-both sides have same moles, so shifting eq. has no effect
RP5a - how would you investigate the RoR as concentration changes based on the volume of gas produced from a reaction?
-add HCl of a specified concentration into a conical flask
-set up apparatus as shown in diagram
-add an Mg strip to flask and quickly close bung while starting a stopwatch
-record volume of gas every 10 seconds by reading the graduations on the measuring cylinder and stop when no more gas is released
-repeat with at least 5 concentrations and plot graph of volume of gas released vs time with a new curve for each concentration
RP5a - Name 2 pieces of apparatus that are necessary in order to find the rate production of hydrogen gas:
-gas syringe
-stopwatch
RP5a - describe the disadvantages of collecting gas over water and using a gas syringe to calculate the RoR:
(same disadvantages for gas syringe method)
-gas could escape before bung is inserted
-some gases can dissolve in the water (CO₂, O₂, Cl₂)
RP5b - how would you calculate the RoR as concentration changes when there is a colour change?
-a volume of sodium thiosulfate into conical flask, and dilute (with water) with 50-the volume of sodium thiosulfate used
-put the flask on a paper with a black cross on it and add HCl and swirl the flask
-start the stopwatch and look down from the top until you can’t see the cross anymore and record the time
-repeat but use less sodium thiosulfate and more water at least 5 times to adjust its concentration
-plot time taken vs volume of sodium thiosulfate used
Give 2 ways you could measure the volume of gas produced from a reaction:
-upside down measuring cylinder with delivery tube
-gas syringe
What does [x] mean?
eg [HCl]
the concentration of substance x
in moles per dm³
When calculating rate of reaction, what should you ensure that your number at the end is?
-positive and a decimal (not fraction)
-rate of reaction is always positive, as a reaction is going from reactants to products
What should you say when a question asks about equilibrium positions?
-say which direction the equilibrium shifts in
-don’t just be vague and say “in the endothermic direction”, say “left/right”
A reaction between calcium carbonate chips and hydrochloric acid occurs, and the rate decreases over time. Explain why:
-acid particles used up so concentration decreases (and SA of calcium carbonate chips decreases)
-less frequent collisions
-less frequent successful collisions
-RoR decreases
