C8 - Rates and Equilibrium Flashcards
Method for disappearing cross experiment
- Use a measuring cylinder to add 10cm3 of sodium thiosulfate into a conical flask
- Place flask onto a printed black cross
- Add 10cm3 of HCl
- Swirl the solution and immdiately start the timer and look down through the top of the flask
- Stop the timer once it has gone cloudy (due to sulfur precipitate) and you can no longer see the cross
- repeat with different concentrations of sodium thiosulfate
- repeat to find a mean
Method for volume of gas produced by a reaction experiment
- Use a measuring cylinder to add 50cm3 HCl to a conical flask
- Attach a bung and delivery tube into a trough of water and and upturned measuring cylinder filled with water
- Add 3cm Mg ribbon
- Swirl + immediately start the timer once the bung is on
- Every 10s, measure the volume of gas collected until it is full
- Repeat to find a mean
- Repeat with different conc. HCl
- Control temperature, length of Mg and volume of HCl
- To find the rate, you do 1/time
What is a reversible reaction?
Where products can react together to form the reactants. There is both a forward, and reverse reaction that can occur
What is dynamic equilibria
where the forward reaction happens at the same rate as the reverse reaction. The concentration of reactants and products remains unchanged
Define the activation energy
- The minimum amount of energy that particles have to collide with for there to be a reaction (successful collision)
Role of a catalyst
- Speed up the rate of reaction
- By providing an alternate reaction pathway
- That requires a lower activation energy
- They are not used up in the process so can be used to speed up the rate of many reactions
- They have alower reactivity that the reactants used so that they don’t interfere with the reaction
How to calculate the mean rate of reaction
- mean rate of reaction = quantity of reactant used/time take
- OR mean rate of reaction = quantity of product made/time take
What does collision theory state
- Particles must collide with each other for chemical reactions to occur
- These reaction can only occur when the particles collide with sufficient energy above the activation energy
Factors that affect the rate of chemical reactions
- Temperature
- Concentration
- Pressure
- Surface Area
- Presence of a catalyst
Explain a reaction graph in terms of collision theory
- Initial reactions are rapid as there his the highest concentration of molecules (lost of molecules that can collide
- Over time, reactions slow down because the reactant molecules have already reacted so there are less collisions per second
- Eventually, the reaction stops becuase there are no collision eper second due to all of the rectant moleucles having been used up
What happens to the rate of reaction if the concentration is doubled
- The nuber of reactant particles in a given volume is doubled
- This doubles the chances of a successful collision (frequency of successful collisions doubles)
- Therefore, the rate of reaction doubles (and it takes half the time)
What does Le Chatelier’s Principle state
Whatever you do to a system in equilibiria to change the reaction conditions, the system will respond to counteract the change. It does this by shifting the equilibria position
What does increasing temperature do to the rate of reaction
- There are more collision (collision rate increases) as the particles move faster
- It also increases the energy of reacting particles
- This means a greater proportion of the particles will have sufficient energy over the activation energy so more succesful collision will occur
- These both mean that the rate of reaction increases
What does increasing the SA do to the rate of reaction
- More particles are exposed to the acid
- This means that more collisions can occur in a set amount of time (frequency increases)
- This therefore increases the chances of successful collisions so the rate of reaction increases
What is a closed system
- Where reactants and products can neither be added nor removed
