rate and extent of chemical Flashcards
what formula can be used to calculate the rate of a chemical reaction
rate of reaction formulas:
- amount of reactant used / time
- product formed / time
- moles of reactant used / time
- moles of product formed / time
What is the equation to find out the mean rate of a reaction?
Mean rate of reaction = quantity of reactant used / time taken
What are the five factors that affect the rate of a chemical reaction?
- Temperature
- Surface area of solid
- Concentration of solutions
- Pressure of gases
- Presence of catalyst
What is collision theory?
states that chemical reactions can only take place when reacting particles collide with each other
- the collisions must have sufficient energy
How can you make reactions more likely to happen between reactant particles?
- Increase the frequency of reacting particles colliding with each other
- Increase the energy they have when they collide
How does a bigger SA:V ratio affect the rate of a chemical reaction?
Increases it, because the frequency of collisions between the reacting particles increases - if solid reactants are in smaller pieces they have a greater surface area
How does increasing the concentration of a solution affect the rate of a reaction?
Increases it, as it increases the frequency of collisions between particles
How does increasing gas pressure affect the rate of a reaction?
Increases it, as the number of gas molecules in the same volume is increased and so increases the frequency of succesfull collision and therefore increases rate of reaction
What is a catalyst?
A substance that increases the rate of a reaction without being used up
How do catalysts work?
They increase rates of reaction by providing an alternative reaction pathway for reactants and lowering the activation energy the particles therefore need less energy to surpass the activation energy, so there are more successful collisions
What are advantages of catalysts?
they allow us to carry out reactions quickly without raising the temperature, saving money
- they can also be reused
- different reactions need different catalysts
What is a reversible reaction?
A chemical reaction where the products can react to produce the original reactants again
If a chemical reaction is endothermic, what is the reverse reaction?
Exothermic
What is dynamic equilibrium?
in a closed system when the forward and backward of a reversible reaction are happening at the same rate and the concentrations of reactants and products remain constant
What is Le Chatelier’s principle?
If a system is at equilibrium and a change is made to any of the conditions, the system responds to counteract the change
What happens if the temperature of a reaction at equilibrium is decreased or increased?
if the temperature of a system at equilibrium is increased:
- the products of the endothermic reaction will increase
- the products of the exothermic reaction will decrease
- the equilibrium will shift towards the product of the endothermic reaction, to decrease the temperature
if the temperature of a system at equilibrium is decreased:
- the products of the endothermic reaction will decrease
- the products of the exothermic reaction will increase
- the equilibrium will shift towards the product of the exothermic reaction to increase the temperature - The exothermic reaction would be favoured
What would happen if the concentration of reactants in a reaction at equilibrium was increased?
- if the concentration of one of the reactants or products is changed, the system is no longer at equilibrium
- the concentrations of all the substances will change until equilibrium is reached again
- if you increase the concentration of the reactant, more of the product will be formed
- if you decrease the concentration of the product, more of the reactant will react
- The reaction would favour the other direction, shifting the equilibrium to generate more products
What would happen if the pressure of gases in a reaction at equilibrium was increased?
for gaseous reactions at equilibrium:
- An increase in pressure = cause the equilibrium position to shift towards the side with the smaller number of molecules
- A decrease in pressure = cause the equilibrium position to shift towards the side with the larger number of molecules
- if the number of molecules on both sides is equal, changing the pressure will have no effect on the equilibrium position
describe the effect of a catalyst on the position and rate of equilbrium
No, catalysts do not affect the position of equilibrium; only the rate of the forward/backward reactions are sped up equally ( equilibrium achieved faster )
explain the shape of the graph for a reactant product graph
- reactions are rapid initially because we have a large number of reactant molecules = there will be a large number of collisions per second
- over time reactions slow down because the number of reactant molecules are running out = there is a smaller number of collisions per second
- reaction stops because all of the reactant molecules have run out = number of collisions per second = 0
what are 3 ways of measuring rate of reaction
- loss in mass of reactants
- volume of gas produced
- time for a solution to become opaque
what is an enzyme
a molecule that acts as a catalyst in a biological system
Using a graph, how can you tell if it has a faster reaction
- higher concentration = faster reaction
- easy to see because line is steeper
what is the result of the product if there is a higher concentration of reactant
more product at the end - as there are more reactant molecules at the start and so there are more reactant particles moving together and there will be more collision so reaction rate increased
Describe the required practical using sodium thiosulfate - disappearing cross experiment
sodium thiosulfate solution + hydrochloric acid –> sulfur
- sulfur makes the solution go cloudy ( also known as turbidity)
1) use measuring cylinder to measure 10cm³ of sodium thiosulfate solution into a conical flask
2) place conical flask on printed black cross
3) add 10cm³ of hydrochloric acid into conical flask
4) swirl solution and start a stopwatch
5) look down at the top of the flask, after some time the solution should start to turn cloudy
6) stop the clock when you no longer see the cross
7) carry out experiment again, with lower concentrations of sodium thiosulfate solution
8) repeat whole experiment, and calculate mean values for each concentration of solution
how can we determine if a measurement if reproducible
- if it can be repeated by another person or using a different technique or equipment and still get the same result
what is an issue with the disappearing cross experiment
different people have different eyesights = some people can see cross for longer than others so they might not get the same results
describe the effect of concentration on reaction rate - using magnesium
magnesium + hydrochloric acid -> magnesium chloride + hydrogen
- the reaction produces hydrogen gas = allows us to measure the volume of hydrogen gas produced
1) use measuring cylinder to measure 50cm³ of hydrochloric acid into a conical flask
2) attach conical flask to a bung and delivery tube, and place the tube in a container full of water
3) place upturned measuring cylinder also filled with water over the delivery tube
4) add 3cm strip of magnesium to hydrochloric acid, and start a stopwatch
5) the reaction produces hydrogen gas, which is trapped in the measuring cylinder
6) every ten seconds, measure volume of hydrogen gas in measuring cylinder, and continue until no more hydrogen is given off
7) repeat experiment with different concentrations of hydrochloric acid
- the greater the concentration of a chemical in a reaction, the faster the reaction takes place
what does frequency mean
the number of successful collision per second
the particles in solution can only react with ?????????
particles on the surface of the solid
which block has a greater surface area to volume ratio: the smaller sized blocks or larger sized blocks
smaller sized blocks have a greater SA: V ratio = more particles on the surface = more collisions per second = increases rate of reaction
what is the activation energy
the minimum amount of energy that the particles must have in order to react
what does the size of the arrow on the particles show
shows the energy of each particle
what would be the result if two particles which have only a small amount of energy collide with eachother
- Because they have low energy, they cannot overcome the activation energy barrier = not collide successfully and no reaction would occur
what would be the result if two particles which have a large amount of energy collide with each other
- they have enough energy to overcome the activation energy barrier and collide successfully = reaction would take place
What will increasing the temperature do to the rate of reaction and why
increases it
- as increasing the temperature increases the energy of the particles - because the paticles now have more energy they now move faster = increases the frequency of collision and there will be a greater number of collisions per second
AND
Each collision now has more energy = more particles can overcome the activation energy barrier and collide successfully
what is the relationship between rate of reaction and temperature
directly proportional to each other
as RATE OF REACTION INCREASES WITH TEMPERATURE
when ammonium chloride is heated what are the products
ammonia + hydrogen chloride
when ammonia + hydrogen chloride are cooled what is the product
ammonium chloride
what type of reaction does ammonium chloride use
reversible reaction - the products can react to reform the original reactants
how can the direction of reversible reactions be changed
by changing the conditions eg
the reaction can go forwards by heating and or the reaction can go backwards by cooling
what is the product when hydrated copper sulfate is heated
reacts to form anhydrous copper sulfate ( which is white ) and also produces water
what is the equation linking hydrated copper sulfate and heat
hydrated copper sulfate ->–<( heat ) anhydrous copper sulfate ( white ) + water
what type of reaction occurs when a substance is heated
endothermic - because energy is being put in
if a reversible reaction is exothermic in one direction what is the reaction in the other direction
endothermic
what happens to the energy transferred in an forward and backward endothermic and exothermic reaction
the same amount of energy is transferred in each case
what is equilibrium
the point at which the forward and reverse reactions take place at exactly the same rate
