C5 - Hell but early Flashcards
Explain what is meant by a closed system.
A system where reactants and products are neither removed nor added.
What happens to the concentration of the reactants and products when dynamic equilibrium is reached?
They stop changing.
How does the equilibrium position change if pressure is increased?
If pressure is increased, then the equilibrium position will shift to the side with the fewest moles, as it will move to the side that will reduce the pressure.
How does the equilibrium position change if pressure is decreased?
The position will shift to the side that will increase the pressure to counteract the external change, so the side with the most moles.
How does pressure affect equilibria with equal numbers of moles on either side of the equation?
It has no effect.
What would happen to the equilibrium position if the concentration of the products is decreased?
The reaction is no longer at equilibrium, so the forward reaction would increase to counteract the change.
What would happen to the equilibrium position if the concentration of the reactants was increased?
The reaction is no longer at equilibrium, so the forward reaction increases so more product is made to counteract this change.
If the forward reaction of an equilibrium is exothermic, what would the effect be on the position if the temperature is increased?
The backwards reaction would increase to counteract the change.
If the forwards reaction is exothermic, what would the effect be on the position of the equilibrium if the temperature is decreased?
The position would shift to the products’ side.
What colours does methyl orange turn in titration?
Methyl orange in yellow when alkaline and red when acidic.
How do you read the volume of solution added by the burette?
Read from the bottom of the meniscus with your eye level with the liquid.
What is meant by concordant results?
Results within 0.1 cm^3 of each other.
Which practical investigates the effect of concentration on the rate of reaction?
The “disappearing cross” practical.
What is the independent variable and the dependent variable in the “disappearing cross” PAG?
Independent - the concentration of sodium thiosulfate solution.
Dependent - the time taken for the cross to disappear.
Outline how to set up the “disappearing cross” experiment.
Place a conical flask over a sheet of plain white paper with an X drawn on it. Pour sodium thiosulfate solution into the conical flask. Ensure that the cross is visible.
Then pour in a known concentration of hydrochloric acid.
Outline how to conduct the disappearing cross experiment.
1 - Set up a conical flask filled with sodium thiosulfate solution over a sheet of plain white paper with a cross drawn on it.
2 - Ensuring the cross is visible at the start, pour in a known concentration of hydrochloric acid and start the timer.
3 - Stop the timer when the cross disappears entirely from view, when the reaction is complete.
4 - Repeat the experiment with different concentrations of sodium thiosulfate solution, and plot the results on a graph.
Which PAG is carried out to investigate the effect of surface area on reaction rate?
Measuring carbon dioxide gas produced from marble chips.
Outline how you would set up an experiment to investigate the effect of surface area on rate of reaction.
1 - Put 50cm^3 of hydrochloric acid in a conical flask, attached to a bung and delivery tube feeding into a gas syringe.
2 - Place marble chips in the conical flask and record how much gas is produced every five seconds. (Marble chips will react with hydrochloric acid, forming carbon dioxide gas that will travel through the delivery tube and be measured in the gas syringe.)
3 - Repeat the experiment with marble chips of different surface areas.
In the surface area RoR PAG, what is the independent variable and dependent variable?
Independent - the surface area of the marble chips.
Dependent - the volume of gas produced every five seconds.
Define a catalyst.
A catalyst increases the rate of reaction by lowering the activation energy by finding an alternative pathway in the reaction.
Give some advantages to catalysts.
- Catalysts are not reactants, so the products are still pure.
- Catalysts are unchanged by reactions, so can be used again and again.
Give some disadvantages to Catalysts.
- Expensive
- Different reactions require different catalysts, so it’s not a one-size-fits-all situation. Different catalysts may be difficult to obtain.
How is rate of reaction measured?
It is the number of successful collisions per second.
What is collision theory?
Collision theory states that a reaction can only take place if particles collide frequently and successfully (meeting the required level of activation energy).
How does temperature affect reaction rate?
As the temperature increases, so does the rate of reaction. This is because a rise in temperature means a rise in internal energy for each of the particles involved in the reaction. The thermal energy from temperature converts to kinetic energy in the particles, causing them to move faster. This increases the frequency of collisions; the rise in energy of the particles also helps to overcome the activation energy requirement, leading to more successful collisions occurring.
This all increases the rate of reaction.
How does concentration affect reaction rate?
As the concentration increases, the rate of reaction also increases. This is because an increase in concentration also means an increase in number of particles in a given volume - the more particles there are in a set volume, the more frequent collisions there will be between these particles. The more frequent collisions there are, the more successful collisions there will be, leading to an increase in rate of reaction.
How does surface area affect reaction rate?
Particles in a solution can only react with the particles on the surface of a solid. The greater the surface area, the greater the number of exposed particles able to collide with particles in solution successfully.
