C5.2 Flashcards
Gas syringe volume of gas (much easier then upturned cylnder used to find rate of reaction)
Attach a side arm flask to a gas syringe , push the plunger to 0
Add the substance and then the magnesium strip and , quickly bung the flask
Start a clock
Read the volume,
Record line graph
Rate of reaction
Mean rate from a graph
Instanwtauenous rste at one post
= amount of product / time or reactant
2) draw a straight line from two pints calculate the gradient
3) tangent to one curve and find gradient. Make sure the axis is reactant or product over x time (volume of gas)
What needed for a reaction to happen successfully ?
- collide - collide with enough energy to react = successful
Why do reactions go faster at higher temperatures (2 ways)
Reactants gain more kinetic energy and therefore move more quickly, leading to more FREQUENCY collisions,
More of the share of reactants gain the activation energy, so more collisions are succesful too. Therefore increasing temperature leads to more collisions and more collisions being successful, meaning rate of rsscrion increase
Rate of recstion is connected to resction time how
As longer it takes less reaction time you can use this as a measure of the reaction rate
Rate of reaction = 1/ resction time
Rate of reaction is inversely proportional to resction time
At higher concentration why does rate of reaction increas
The more concentrated the solution is, the more the reactants (particles) are crowded (as more particles in Same volume , so likely to react with each other more, leading to more frequent collisions and therefore more successful collision= higher rate of reaction
Why do reactions go faster at higher presssure.
When you increase pressure, the particles in gas state become more crowded, so they collide more often, leading to more frequent collisions and therefore more successful collisions, higher rate of reaction
Investigate concentration effecting the rate of reaction
What must we control
Use HCL and magnesium ribbon.
Measure the time it takes for the msgenisum ribbon to be fully reacted ,
then do 1/ time to get rate of reaction.
Change the concentration of the acids by diluting them more or less with water.
Control length of magnesium, volume of acid, the amount of ,sss is proportional to the time taken so yh
Why do reactions rate higher for powders?
Powdered substance have a higher surface area in the same volume, this means more particles are available for reaction at a given time and this leads to more frequent collisions, and therefore succesful collisions and so a higher rate of reaction
Investigating particle size.
1) React different levels of powder with acid, so ca co3 for example. With HCL
2) use a flask and cotton wool covering the top, lets gasses through but not any liquid solid or aqueous out coming from the mixture.
When the cao3 reacts, carbon dioxide escapes which is shown in the mass readings, start a clock. And now calculate reaction time
Use different powders
Control the mass because more mass means more can react
Catalysts
What do they do
Where are they used, why honeycomb good
Hoe to investigate catalyst
Biological catalyst?
Catalysts increase the rate of reaction of a substance without being used up. Meaning once catalysed it can catalysed something else
It offers an alternative reaction pathway that uses less activation energy, this means that a greater proportion of the particles will now have the activation energy required , meaning more successful collisions and higher rate if reavtion .
A small amount of catalyst will do a lot- good for it because they expensive. Platinum rhodium etc
These are coated onto a honeycomb, giving them higher surface area den let’s exhaust gases thieugh
2) hydrogen peroxide in solution connected to gas syringe and then add catalyst .
If reaction increases after compared to before
And you can retrieve it later and it’s not changed then it is. Do this by ensuring mass is the same .
Control everything because then you know that was the catalyst who helped no one else.
- works in biological systems
Reversible reactions
What is dynamic equilibrium
In a reversible reaction the products can react to form the reactants again
Dynamic equilibrium is where the the forward rate of reaction = the backward rate of reaction . The concentrations of the products and reactants are as a result NOW fixed but not necessarily in SAME QUANTITIES . This can only happen in a CLOSED SYSTEM
Le dhatelier’s principle
Pressure, temperature, concentration
When a change happens to a reaction in equilibrium , the position of equilibrium moves to oppose the change
1) when pressure (gas) is increased, the equilibrium position moves to the side with lowest moles of gas, to reduce the pressure
2) if temperature is increase the equilibrium position will favour the endothermic reavtion, if temp decrease,will favour the exothermic
3) if concentration increase, equilibrium position moves away from that substance to make more opposite so more is used up, decreasing amount of particles of increased concentration
Decrease concentration of reactant and it move to the reactant to increase concentration of that
Measure temperature affects rate. Using yellow predication?
1) mix recatants in beaker where underneath is a cross
2) the quicker it takes for the cross to disappear the quicker rate of reaction
3) subjective but vary temperatures to investigate these…
When investigating graphs of reacting time being affected by a condition remember that line will reach more quickly because everything has been reacted now!!
A
Reaction experiments summarised
1) predication one , where time how long for x to go, use in temperature investigating
2) change in mass, where cotton ball allows carbon dioxide or hydrogen through, you can use concentration
3) volume of gas is old reliable , use for powdered chips and ctalatsyst and anything give a gas
