Section 5 - Kinetics, Equilibria and Redox Reactions Flashcards
Define reaction rate
Change in concentration/amount of a reactant or product over time.
What is the formula for rate of reaction?
Amount of R used or P formed/time
What are the two conditions that allow a reaction to take place when particles collide?
- right direction - activation energy
Define activation energy
Minimum amount of kinetic energy required for particles to react upon collision.
What does a Maxwell-Boltzmann distribution show?
The number of molecules in a gas against their kinetic energy.
What is the area under a Maxwell-Boltzmann distribution?
The total number of molecules.
Why does a Maxwell-Boltzmann curve start at (0,0)?
0 molecules will have 0 energy
What does the peak of the Maxwell-Boltzmann curve show?
The most probable energy of any molecule.
Where is the mean energy of all of the molecules in a Maxwell-Boltzmann curve?
Slightly to the right of the peak.
Where would you find the section of molecules with the required activation energy on a Maxwell-Boltzmann curve?
On the right.
What happens to the average kinetic energy if the temperature of a reaction is increased?
It will increase.
What happens to the proportion of molecules with the required activation energy if the temperature of a reaction is increased?
It will increase.
How does the Maxwell-Boltzmann curve change when temp is increased?
- shifts to right - peak is smaller
Why does rate of reaction increase with temp?
- molecules have more energy - more have Ea required - move faster - collide more often - more likely to react
Why does rate of reaction increase with concentration?
- particles closer together - collide more often - more likely to react
Why does rate of reaction increase with pressure?
- particles closer together - collide more often - more likely to react
Why does rate of reaction increase with a catalyst?
- provide alternative route with lower Ea - more particles have enough energy to react - more likely to react
Define catalyst
A substance that increases the rate of a reaction by providing an alternative reaction pathway with a lower Ea. It is chemically unchanged at the end of the reaction.
Why are catalysts good in industry?
- don’t get used up (small amount required) - work faster - allow a lower temp
Give 3 ways to measure reaction rates:
1) Timing how long a precipitate takes to form 2) Measure a change in mass 3) Measure vol of gas given off
Give a negative of timing how long a precipitate takes to form
Subjective
Give a pro and con of measuring a change in mass
+ accurate and easy - releases gas
Give a pro and con of measuring vol of gas given off
+ accurate - only works if one or more product is gaseous
Give an example of a reaction that forms a precipitate
Sodium Thiosulfate and Hydrochloric Acid
What do Sodium Thiosulfate and Hydrochloric Acid react to form and what is observed?
Sodium Thiosulfate and Hydrochloric Acid are both clear solutions which react to form a yellow precipitate of sulfur.
What is the experiment between Sodium Thiosulfate and Hydrochloric Acid usually used to investigate?
The effect of increasing temperature on reaction rate.
How do you react Sodium Thiosulfate and Hydrochloric Acid?
- Measure out fixed vols of each in measuring cylinders - Use a water bath to heat each to desired temp - Mix solutions in conical flask - Place flask over black cross and time until it isn’t visible
What is a reversible reaction?
A reaction that can occur in both directions
What is a dynamic equilibrium?
When the forward reaction is happening at the exact same rate as the backward reaction.
What is the condition for a dynamic equilibrium?
A closed system
What is Le Chatalier’s principle?
If a reaction at equilibrium is subjected to a change in concentration, pressure or temperature, the position of the equilibrium will move to counteract the change.
What has to be the same about reactants and products for La Chatalier’s principle to apply and what is this called?
They have to be in the same physical state - homogeneous equilibria.
What effect does increasing the concentration of a reactant have on the equilibrium?
Shifts it to the right
What effect does increasing the concentration of a product have on the equilibrium?
Shifts it to the left
What effect does decreasing the concentration of a reactant have on the equilibrium?
Shifts it to the left
What effect does decreasing the concentration of a product have on the equilibrium?
Shifts it to the right
What effect does increasing the pressure of a reaction have on the equilibrium?
Shifts to the side with fewer moles
What effect does decreasing the pressure of a reaction have on the equilibrium?
Shifts it to the side with more moles
What effect does increasing the temperature of a reaction have on the equilibrium?
Shifts in the endothermic direction
What effect does decreasing the temperature of a reaction have on the equilibrium?
Shifts it in the exothermic direction
What effect does using a catalyst have on the equilibrium?
No effect.
What is Kc?
Equilibrium Constant
What is the expression for Kc?
aA + bB ⇌ dD eE
Kc = [D]d[E]e/[A]a[B]b
How do you calculate units for Kc?
Put units into expression and cancel.
What condition is Kc dependent on?
Temperature
If temp change forms more product, how is Kc affected?
It increases
If temp change forms more reactants, how is Kc affected?
It will decrease.
If concentration is changed, how is Kc affected?
No change
If a catalyst is used, how is Kc affected?
No change.
What happens during oxidation?
Loss of electrons
What happens during reduction?
Gain in electrons
What happens in a redox reaction?
Oxidation and reduction occur simultaneously.
What does an oxidising agent do?
Accepts electrons and gets reduced.
What does a reducing agent do?
Donates electrons and gets oxidised.
What does the oxidation state of an element tell you?
The total number of electrons it has donated or accepted.
What is the oxidation state of elements?
0
What is the oxidation state of elements bonded to identical atoms? (eg. O2)
0
What is the oxidation state of a simple monatomic ion?
Same as its charge.
What is the oxidation state of compound ions?
Same as the ion charge
What is the oxidation state of a neutral compound?
0
What is usually the oxidation state of combined oxygen?
-2
What is the oxidation state of combined oxygen in peroxides?
-1
What is the oxidation state of combined hydrogen usually?
+1
What is the oxidation state of combined hydrogen in metal hydrides?
-1
What do Roman numerals tell you about a chemical?
Its oxidation state
What do ionic half equations show?
Oxidation or Reduction
