Reaction Rates Flashcards
A + B →
C + D
Define reaction rate
number of moles of product formed per second.
or
number of moles of reactant used per second
What is the unit for reaction rate
mol / s
What are the 4 methods for reaction rates
1) mass change
2) volume of gas
3) solid disappearing
4) color change
What is the reaction rate represented by on a graph?
the gradient
Define tangent
straight line that has the same gradient as 1 point on a curve
What is one way mass change can be measured?
What would you measure?
by measuring the volume of gas made / used up
Why does the mass decrease when measuring mass change in a reaction between metal carbonate and acid?
because gas is produced, and as it goes out of the top of the conical flask and therefore the mass left in the flask is less than what is started at
Why shouldn’t you measure the initial volume of gas produced when measuring volume of gas?
because no gas is produced initially
What does a graph of measuring the mass change in a reaction with a metal carbonate and an acid look like?
add photo at home
What does a graph of measuring the volume of gas in a reaction with a metal and an acid look like?
and tangent
add photo at home
and tangent
What would you measure in a reaction of solid disappearing?
time until solid disappears
What are the problems with using solid disappearing as a rate of reaction?
- can only calculate average rate
- no graph
What would you measure in a reaction of color change?
time until color change is observed
What are the problems with using color change as a rate of reaction?
- no graph
- can only calculate average rate
- subjective
Give an example of a color change reaction
iron (gray) + copper sulfate (blue) → iron (II) sulfate (green) + copper (orange)
What apparatus is needed when measuring volume of gas?
- gas syringe
Describe the ‘flow’ of a rate of reaction from beginning to end
the rate always decreases from beginning to end
Why does the rate of reaction decrease?
because the rate of collisions decreases
What happens when when reactants are used up during a reaction?
fewer particles are available
What happens at the end of a reaction?
there are no more reactants available therefore no collisions can occur
What do particles have to do in order for a reaction to happen?
they have to collide
What 2 properties are needed for particles to be able to collide?
1) sufficient energy
2) correct orientation
What is energy used for in a reaction?
to break the bonds of the reactants
Are most collisions successful or unsuccessful?
unsuccesful
What can be done to increase rate of reaction?
1) increase frequency of collisions
2) increase the proportion of successful collisions
What can be done to increase the proportion of successful collisions?
1) change energy of particles
2) change orientation of particles
What 4 factors affect rate of reaction?
1) temperature
2) surface area
3) catalysts
4) concentration / pressure
Write a general method for measuring the effect of surface area of a rate of reaction
1) measure x cm³ (25 cm³) of HCL into a conical flask using a measuring cylinder
2) record mass of apparatus
3) record mass of CaCO₃
4) add CaCO₃ to HCl on a balance
5) start timing
6) record mass every 20 seconds until the reaction ceases
7) repeat with equal mass of CaCO₃ powder
What will increasing the temperature do to a rate of reaction?
increase the rate of reaction
What 2 factors make increasing the temperature increase the rate of a reaction?
1) particles gain kinetic energy, move faster and collide more frequently (this effect is minor, there is only a slight change in collision frequency)
2) proportion of particles with Ea is increased
Does an energy profile indicate rate of reaction?
no
Does the energy change depend on the rate of reaction?
no, the energy change will be the same regardless if the reaction occurs faster or slower
Define Ea
the minimum energy required for particles to react (energy needed to break bonds in reactants)
What are the axis in a Maxwell - Boltzmann distribution graph?
X - axis - energy
Y - axis - frequency / number of particles
Explain and Describe the Maxwell - Boltzmann distribution
on the black curve, the part shaded in pink are the particles with enough energy (Ea or 50 kJ / mol) that can collide, with the temperature at 25 ºC. the pink line shows the temperature that was then increased to 50 ºC. now the region in bronze shows that there are more particles with the minimum Ea (50 kJ / mol) available to react. this increases the frequency of successful collisions. this significantly increases the rate of the reaction
Define temperature
the average energy / movement of particles in a sample
Why are most collisions unsuccessful?
because one or both particles have insufficient energy (Ea)
Define catalyst
a substance that increases the rate of a reaction without being used up in a reaction
How can catalysts affect the rate of a reaction?
1) affect the frequency of collisions
2) increase the proportion of collisions with the correct orientation
3) increase proportion of particles with Ea
Most catalysts are heterogenous to the reactants. What does this mean?
catalysts are a different state to the reactants
Is a rate of reaction without a catalyst fast or slow?
slow
