Kinetics Flashcards
When can reactions occur
Only when collisions take place between parties having sufficient energy and correct orientation
What is this sufficient energy called
The activation energy
Activation energy
The minimum energy required to start a reaction by breaking of bonds
Why do most collisions not lead to a reaction
- may be insufficient energy
- orientation may be incorrect
Rate of reaction
The change in concentration of a substance in a given time
What are the units of rate
mol dm-3 s-1
Why does the rate decrease as the reaction proceeds
The concentration of reactant falls
What is the rate at a particular time equal to
The gradient at that time
What is the correlation between concentration and rate
Increasing the concentration increases the rate
Why does increasing concentration increase rate
- more particles per unit volume
- more collisions per second
- faster rate
What is the correlation between pressure of gases and rate
Increasing the pressure increases the rate
Why does increasing pressure gases increase rate
- more particles per unit volume
- more collisions per second
- faster rate
What is the correlation between increasing SA of solids and rate
Increasing SA increases rate
Why does increasing SA of solids increase rate
- more surface of solid exposed to other reactant
- more collisions per second
- rate is faster
What is correlation between temperature and rate of reaction
Increasing temperature increases the rate
Why does increasing temperature increase rate
- more particles have energy equal to or greater than activation energy
- more successful collisions
- rate is faster
What does adding a catalyst do to rate of reaction
Increases it without it being used up
Why does adding a catalyst increase rate of reaction
- provides alternate pathway
- lower activation energy
- more successful collisions
- faster rate
Experiment between HCl and CaCO3 to show effect of conc on RoR
Add CaCO3 to HCl
Collect CO2 produced in a gas syringe
Record volume of CO2 at regular intervals
Produce graph of volume of CO2 against time
What would a curve look like with same number of moles of acid but higher concentration
Steeper curve but levels of at same volume of CO2
What would curve look like with half moles acid but same conc
Same steepness of curve but half final volume of CO2
What does the reaction between sodium thiosulfate and hydrochloric acid produce
A precipitate of sulfur, sodium chloride and sulfur dioxide
How can the rate of reaction between sodium sodium thiosulfate and hydrochloric acid be monitored
Measure time taken for cross to disappear from view
Cross obscured by PPT of sulfur
What is measuring time taken for cross to disappear called
Initial rate method
How can temp be known as accurately as possible in reaction between sodium thiosulfate and hydrochloric acid
Measure initial and final temp- take and use an average
What could be used to prevent SO2 escaping from the reaction
Put a lid on the reaction vessel to minimise escape of CO2
Why is a STOP bath used in reaction between sodium thiosulfate and hydrochloric acid
Both acid and sulfur dioxide can be neutralised
What is the independent variable in the reaction between sodium thiosulfate and hydrochloric acid
Temperature
What is the dependent variable in the reaction between sodium thiosulfate and hydrochloric acid
Time
Why is the hazard associated with sulfur dioxide in this investigation considered to be low
Amount of SO2 low because solutions are dilute
SO2 is soluble- doesn’t all escape as a gas
Why do the particles in a particular sample have a spread of energies when the samples collide
Energy is exchanged between them
What does the Maxwell-Boltzmann distribution show
The distribution of energies of the particles within a sample
What is the important feature of the maxwell boltzmann distribution that is seen at the origin of the graph
No particles have no energy
What is the important feature of the maxwell boltzmann distribution that is seen at the end of the graph
The curve doesn’t meet back with the x axis- no maximum energy
What is the important feature of the maxwell boltzmann distribution at the highest point of the graph
The most likely every is not very high
What does the shaded area represent on a maxwell Boltzmann distribution
Particles which will successfully collide
How is the peak on a maxwell distribution curve at a higher temperature different
It’s lower and to the right
What is the difference between most probable energy in a maxwell Boltzmann distribution curve at a higher temp
The most probable energy is higher
What is the change in area under the curve maxwell botlzmann at higher temp
Area under curve remains same
How is the shaded area different in maxwell Boltzmann curve at higher temp
Shaded area now much larger as far more particles have energy equal to or greater than activation energy
Why does a small temperature increase lead to a large increase in rate
Far more particles will now have energy greater than or equal to activation energy so far more successful collisions
What is a catalyst
A substance which increases the rate of a chemical reaction without being changed in chemical composition or amount
What does a catalyst provide
An alternative reaction route with a lower activation energy
What is lowered and what is unchanged in the presence of a catalyst
Activation energy lowered but enthalpy not changed
What does a maxwell Boltzmann distribution look like with a catalyst
Shaded area is bigger so more molecules have energy greater than or equal to activation energy
More collisions are successful so rate of reaction increases
