UNIT 1: SECTION 5-KINETICS, EQUILIBRIA AND REDOX REACTIONS Flashcards
(47 cards)
A) Define “reaction rate”
B) Outline the simple formula for finding the rate of a chemical reaction
A)-change in concentration (amount) of reactant or product over time
B)-rate of reaction=amount of product formed/time
A) What are particles constantly doing liquids and gases?
B) Describe collision theory
A)-always moving and colliding with each other
B)-particles not react all the time only when conditions right
–>reaction wont happen unless:
1-they collide in right direction–>need to be facing each other in right way
2-they collide with a minimum amount of K. Energy (movement).
A) Define “activation energy” and briefly explain it
B) What does a high or low activation energy of a reaction mean?
A)-minimum amount of energy particles needs to react with
-the particles must have at least this much energy to break their bonds and start the reaction
B)-low activation energy reactions often happen easier
–>BUT reactions with high activation energies don’t as they particles need extra energy by heating them.
A) What does a “Maxwell-Boltzmann Distribution” curve show?
A)-different molecules in a gas have different kinetic energies
- ->some don’t have much energy and move slowly
- ->others have lots of K.E and whizz around a lot
- ->but most molecules are in between
- if you plot a graph of the n. of molecules in a gas with different kinetic energies you get a “Maxwell-Boltzmann Distribution” curve.
Describe the following parts of the Maxwell-Boltzmann curve:
A) Graph starts at (0, 0) B) Start of graph steepening C) Graph continues to steepen D) Peak of the curve E) Average K. Energy (mean) of all molecules F) Start of shaded part
A)-this as no molecules have no energy
B)-some molecules are moving slowly
C)-most molecules moving at moderate speed–>their energies are somewhere in middle
D)-this represents most likely energy of any single molecule
E)-this may be to the right or left of the peak
F)-activation energy starts
–>area of this shows that some molecules have more than the activation energy
–>these are the only ones able to react.
A) What is the effect of increasing the temperature of a reaction?
B) Why as a result of a temperature increase would the shape of the Maxwell Distribution curve change and how?
A)-if increase the temperature the particles will on average have more K.E and will move faster
B)-so a greater proportion of molecules will have at least the activation energy and so be able to react
–>this changes the curve’s shape–>pushes over to right.
C) Also, how else does a temperature increase on the rate of a reaction?
D) Consequently, what does it mean when you get both of these 2 effects happening at once (increase reaction rate)?
C)-this is as at higher temp as molecules moving about faster they’ll collide more often
D)-more collisions and more energetic collisions means quite a small temperature increase in temperature can lead to quite a large increase in the rate of reaction.
A) Describe the effect of an increase in CONCENTRATION on the rate of reaction
A)-if increase conc of reactants in solution, the particles will on average be closer together
- ->if they are closer together they would collide more often
- ->if collisions more frequent they would have more chances to react
- ->therefore increasing concentration increases reaction rate.
B) Explain the effect of an increase in PRESSURE on the rate of reaction
B)-if reaction involves gases increasing pressure works same way a increasing conc
- ->it pushes all of gas particles closer together
- ->making them more likely to collide
- ->so collisions take place more frequently + reaction rate increases.
C) Define a “catalyst”
C)-a substance that increases reaction’s rate by providing alternative reaction pathway with lower activation energy
–>the catalyst is chemically unchanged end of reaction.
D) Why are catalysts useful?
E) How are catalysts v. specific?
D)-1: they don’t get used up in a reaction so only need tiny bit of it to catalyse lots of stuff
–>do take part in reaction but REMADE at end
2-a catalysts allow you to make same amount of product faster (+ often at lower temp too), they save lots of money in industrial processes
E)-very specific as to which reactions they catalyse
–>often only work on a single reaction.
A) How is the effect of a catalyst shown on a Maxwell-Boltzmann distribution curve?
A)-more particles have at least the activation energy in the catalysed reaction
- ->lower activation means more particles have enough energy to react when they collide
- ->does this via going a different route
- ->so in certain amount of time more particles react
A) Outline and evaluate the method to follow to measure the rate of reaction by TIMING HOW LONG A PRECIPITATE TAKES TO FORM
A)1-can use this method when product a precipitate which clouds solution
2-watch a mark through a solution + time how long takes to be obscured
3-is same observer uses same mark each time, you can compare reaction’s rate as roughly same precipitate amount will have been formed when mark obscures
4-this methods subjective though–>different people may not agree exact moment mark disappears.
B) State the method and evaluate it to measure the rate of reaction by MEASURING A DECREASE IN MASS
B)1-When 1 + products is a gas you can measure rate of formation using mass balance
2-as gas given off–>mass of reaction mixture decreases
3-this method accurate + easy to do
–>but it does release gas into atmosphere so usually done in fume cupboard.
C) What method must you follow to measure the rate of reaction when MEASURING THE VOLUME OF GAS GIVEN OFF? Also evaluate this method
C)1-this involves using gas syringe to measure volume of gas being produced
2-can only use this method when 1 + products is a gas
3-gas syringes usually give volumes to nearest 0.1cm3, so this method is accurate.
A) Describe the reaction between Sodium Thiosulfate and Hydrochloric Acid and the rate of reaction may be measured
A)-sodium thiosulfate + HCl are both clear, colourless solutions
- ->they react to form a yellow precipitate of sulfur
- can use amount of time takes for precipitate formation as measure of reaction rate
- ->this experiment often used to demonstrate effect of increasing temp on reaction’s rate.
B) Describe the method to follow to measure the rate of this reaction
B)1-measure fixed sodium thiosulfate volumes + HCl using measuring cylinder
2-use water bath to gently heat both solutions to desired temp before mixing them
3-mix solutions in conical flask
–>place flask over black cross that can be seen through solution
–>watch cross disappear through cloudy sulfur–>time it
4-can repeat reaction at different temperatures
–>depth of liquid must be kept same each time
–>concentrations of solutions must be kept same too
C) What results should you expect from this experiment?
C)-results should show that higher the temp
–>faster rate of reaction and so takes less time for mark to disappear.
A) What are “reversible reactions”?
B) Outline an example of a reversible reaction
A)-many chemical reactions reversible–>go both ways
–>2 way arrow represents this
B)-H2 (g) + I2 (g)–> 2HI (g) (reaction can go either way)
2HI
H2 (g) + I2 (g)
C) Describe and explain “dynamic equilibrium”
C)1-as reactants in reaction get used up forward reaction slows AND as more product formed reverse reaction speeds up
2-after while forward reaction at exact same rate as backwards so amount of reactants + products not change no more
–>this is dynamic equilibrium because concentrations of reactants + products stay constant
D) What is the link between dynamic equilibrium and “closed systems”?
D)-dynamic equilibrium only possible in closed system
–>this means nothing able to get in or out.
A) What would happen if you change the concentration, pressure or temperature of a reversible reaction?
A)-you would be altering the position of equilibrium
–>mean would end up with different amounts of reactants and product at equilibrium.
What would happen in each of the following reactions?:
A) H2 (g) + I2 (g)–> 2HI (g)
2HI (g)
A)-lots of H2 and I2 but not much HI in reaction
–>so you would get more reactants
B)-not much H2 and I2 but lots of HI
–>so more products
C) Outline “Le Chatelier’s principle” and briefly explain it
C)-if a reaction at equilibrium is subjected to change in concentration, pressure or temperature, the position of of equilibrium will move to counteract the change
- ->so if raise temp, the position of equilibrium will shift to try and cool things down
- ->and if raise the pressure or concentration, the position of equilibrium will shift to try and reduce it again.
