Chemistry Unit #7: Kinetics and Equilibrium .... Test on April 5, 2017 Flashcards
What is the chemical equation of the ignition of nitroglycerin?
C₃H₅N₃O₉(l) ===> 12CO₂(g) + 10H₂O(g) + O₂(g) + 6N₂(g) + energy
Meaning of Q’s value
- if Kc > Q: forward rxn favored - vice versa
Write the equilibrium constant expressions for the following reactions at equilibrium. C) C₂H₅OH(l) + CH₃COOH(l) ⇌ CH₃COOC₂H₅(l) + H₂O(l)
Kc = [CH₃COOC₂H₅] [H₂O] / [C₂H₅OH] [CH₃COOH]
Reversible reactions do not reach an ____. 3
End Never go to completion Final observation in not 100% of product
A catalyst increases the rate of forward and reverse reactions equally.
A catalyst increases the rate of forward and reverse reactions _______.
What is a device that can be used to measure the amount of light absorbed at a particular wavelength — the darker the colour of the sample, the more light is absorbed
A colorimeter
Write the equilibrium constant expressions for the following reactions at equilibrium. A.) 2NH₃(g) + H₂SO₄(g) ⇌ (NH₄)₂SO₄(g)
Kc = [(NH₄)₂SO₄] / [NH₃]² [H₂SO₄]
What does Kc mean?
Equilibrium constant at a particular temperature
What does Nitrogen Fixation naturally? 3
Bacteria do this naturally Good for plants Because it is needed for growth (fertilizer)
Was nitroglycerin, C₃H₅N₃O₉(l) dangerous to handle on its own?
Yes, it was
State the four factors that affect the reaction rate and one that only affects if particle are gases.
Break up solid reactants to increase the Surface area Increase Concentration or Shrink container Increasing the Temperature Adding/Using a Catalyst Increase the number of particles or increase pressure
Slope in a graph _______ as reactant as used up.
Decreases
For the following equilibrium constants, predict which would exist in higher quantities — reactants or products. D) 1.00
Neither reactants or products
What three main things happen when the Reverse reaction is favoured?
Reaction shifts towards the left side More reactants form Amount of products reduced
Reaction rate is the ______ of the reaction
Speed
For an endothermic reaction, the value of the equilibrium constant _________ as the temperature is increased. Why?
For an endothermic reaction, the value of the equilibrium constant increases as the temperature is increased.
Endothermic’s process is A + B + heat = C + D
We treat heat a reactant and because we have more reactants, we make more products, thus shifting the equilibrium to the right/forward
What happens to the Chemicals during Dynamic Equilibrium?
Chemicals shift between reactant side and product side
Is Equilibrium limited to chemical reactions?
No, it is not limited to chemical reactions
State two general ways, according to the collision theory, the reaction rate could be increased.
1) Increase the frequency of collisions (If Obinna’s chance of success is 1%, he will get 1 date from asking 100 women. He can increase his chances by asking 1000 women, with which he will get 10 dates.) 2) Increase the energy with which they collide in a certain time. (Get more Attractive)
State the only factor that when changed will alter the equilibrium constant. Kc
Temperature
Given: C₂H₅OH(l) + CH₃COOH(l) ⇌ CH₃COOC₂H₅(l) + H₂O(l) In which direction will the equilibrium shift if: B) more alcohol is added
Stress: Favoured: Direction: right/forward
How is O₂(g) obtained for the Contact Process reaction of 2SO₂(g) + O₂(g) ⇌ 2SO₃(g) ∆H°= -197 kJ/mol??
From fractional distillation of liquid (compressed) air
In reversible reactions, sometimes products will collide and lead to the reforming of ________
In reversible reactions, sometimes products will collide and lead to the reforming of reactants
How does Nitrogen Fixation happen?
Changing N₂(g) to a nitrogen compound
State two way the rate of a reaction may be defined.
-Increase of concentration of products per unit time -Decrease of concentration of products per unit time
What is the yield rate of the Contact Process under the 3 conditions for the optimum yield of sulfuric acid, H₂SO₄(aq)?
99%
Why must a fire in a fireplace be started with paper and kindling instead of lighting the logs directly?
A match does not put out enough energy to get a log up to the temperature where it will burn. It’s easiest to start the fire with something that is easier to light; something thin that has a lot of surface area to react with oxygen and cannot conduct the heat of the match away quickly enough to prevent it from reaching combustion temperature.
What is the main reaction of sulfuric acid? (before mixed with water)?
2SO₂(g) + O₂(g) ⇌ 2SO₃(g) ∆H°= -197 kJ/mol
What is a collision called when it results in a reaction?
Successful Or Effective
Define the term “Homogenous reaction”.
A reaction in which all reactants and products are in same phase.
Define Dynamic Equilibrium 3 + example
- Reverse reaction and forward reaction occur simultaneously - the rate of forward reaction is equal to the rate of the reverse reaction - concentrations of reactants and products remains constant Macroscopic properties are constant (concentrations of all reactants and products remains constant) the rate of forward reaction is equal to the rate of the reverse reaction Chemicals shift between reactant side and product side Example: walking up an escalator moving down, still moving but no progress made Exam tip: When asked to define dynamic equilibrium you must address both the “dynamic” and the “equilibrium” part.
What are the requirements to form a dynamic equilibrium? 1 + 4 points on example
Reaction must be reversible and form a closed system — No matter and energy can leave Material (& energy) can neither enter nor leave the container Example: Consider a reversible reaction that forms a gaseous product If the gaseous product escapes to the air, equilibrium cannot be reached Because products will not collide with each other to form the reactants in a certain time. By putting a lid to contain the gas formed, reverse reaction will occur
Describe what is “equal” in a chemical reaction at “equilibrium”.
It refers to the rate of forward and reverse reactions.
difference between Kc and Q
Kc: describes rxn at equilibrium Q: describes rxn not at equilibrium
If K is a large number, it means that the equilibrium concentration of the reactants is _______. In this case, the reaction as written will proceed to the _______
If K is a large number, it means that the equilibrium concentration of the reactants is small. In this case, the reaction as written will proceed to the left (resulting in an decrease in the concentration of products)
Where can Equilibrium also exist, besides chemical reactions? 1 + 5 points on Example
physical equilibrium Equilibrium also exists in physical changes Example: Equilibrium between condensation rate & evaporation rate in a closed bottle An exchange of state with water between liquid and vapour Written as H₂O(l) ⇌ H₂O(g) Liquid water is “in equilibrium with” gaseous” gaseous water Water will not completely evaporate if bottle is kept sealed
What was the energy put out by the main chemical reaction of the Haber Process?
N₂(g) + 3H₂(g) ===> 2NH₃(g) ∆H°= -92 kJ/mol
State how changing the Surface area of solid reactants as one of the four factors that affect the reaction rate and provide: A) an explanation why it causes the rate to increase and B) an example of each 6
Reactions generally only occur at the surface of a solid. Making a solid more finely divided increases the surface area and therefore the number of particles exposed at the surface. The effective concentration of the particles of the solid has thus been increased and there is a greater chance of a particle of the other reactant colliding with a particle on the surface and reaction occurring. Powdered reactants react faster When there is a low surface area, only the particles on the outside are exposed on the surface and able to collide with the particles in a certain time. When there is a high surface area, all the particles are exposed and are able to collide with the particles in a certain time. Example: Dissolving sugar cubes vs sugar grains Melting ice cube vs. ice chips
Where are Catalysts written above?
written above the yield arrow
State the conditions needed for the optimum yield of ammonia in the Haber process. Justify why these conditions are used. 4
1) High concentrations of N₂(g) and H₂(g) ➽ The ratio is always maintained at a ratio of 1:3 to make sure there is no limiting reactant and effective collisions are increased. 2) Use of catalyst - heated powdered iron oxide ➽ Heated powdered iron oxide is used because being powdered increases surface area for the reaction and being heated means that particles have more energy and collide harder, thus making sure there are a lot of effective collisions in a certain time. 3) Removal of Ammonia ➽ This drives equilibrium forward. 4) Ideal temperature is 450°C ➽ This ideal temperature is balances between high equilibrium yield and a faster reaction rate.
How do you find the average rate of a reaction from looking at a graph?
Average Rate = (change in volume/mass/concentration) / (time)
Reversible reaction form an equilibrium ______
System
Given: 2NO(g) + O₂(g) ⇌ 2NO₂(g) ∆H°= -2.7 kJ/mol What will happen to the concentration of NO₂(g) for each of the following. A) adding more NO(g)
Stress: Favoured: concentration of NO₂(g) goes up
Given: 2NO(g) + O₂(g) ⇌ 2NO₂(g) ∆H°= -2.7 kJ/mol What will happen to the concentration of NO₂(g) for each of the following. B) temperature is increased
Stress: Favoured: concentration of NO₂(g) goes down
What is the kJ/mol energy of the triple bond of a molecule of nitrogen?
A strong triple bond (941 kJ/mol)
Catalysts do not appear as a ________ or _________
Catalysts do not appear as a reactant or product May be written above the yield arrow
State the conditions needed for the optimum yield of sulfuric acid in the Contact process. Justify why these conditions are used. 3
1) High pressure - 3 moles of gas forming two moles of gas …………………………- 2 atm used ↠ The production of H₂SO₄(aq) requires the reaction of 2SO₂(g) + O₂(g) ⇌ 2SO₃(g). Where SO₂(g) is obtained from burning sulfur or sulfide ores and O₂ is obtained from fractional distillation of liquid (compressed) air. Using high pressure shifts the reaction to the right, making more SO₃(g). SO₃(g) is then added with water to finally make H₂SO₄(aq). 2) Ideal temperature is 450°C ↠ 450°C is an ideal high temperature that favours the reverse reaction, which increase the reaction rate. 3) Adding vandaium (V) oxide as a catalyst ↠ Adding the catalyst increases rate without affecting equilibrium. ⇝ The yield rate at these conditions is 99%. Using a higher pressure would be uneconomical
situation where Kc won’t apply
non-reversible rxns
Given: CO₂(g) + H₂(g) ⇌ CO(g) + H₂O(g) ∆H°= +41 kJ/mol In which direction will the equilibrium be shifted by each of the following changes? E) temperature is increased
Stress: Favoured: Direction: right/forward
A second order reaction will increase _______ 2
A second order reaction will increase non-linearly (quadruple) Increasing in a curve line
Given: CO₂(g) + H₂(g) ⇌ CO(g) + H₂O(g) ∆H°= +41 kJ/mol In which direction will the equilibrium be shifted by each of the following changes? D) increasing the pressure
Stress: Favoured: Direction: no effect
Given: 2NO(g) + O₂(g) ⇌ 2NO₂(g) ∆H°= -2.7 kJ/mol What will happen to the concentration of NO₂(g) for each of the following. C) increasing the pressure
Stress: Favoured: concentration of NO₂(g) goes up
Bond making releases or absorbs energy?
Bond making releases energy
Where is the activated complex or transition state found on an enthalpy level diagram?
It is found in the highest point along the curve
State how changing the Concentration as one of the four factors that affect the reaction rate and provide: A) an explanation why it causes the rate to increase and B) an example of each 3
With more particles in a certain volume, the particles collide more often (the collision frequency is higher) and therefore there is greater chance of a successful collision occurring in a certain time. When there is a lower concentration, the particles are further apart and collide less frequently in a certain time. When there is a higher concentration, the particles are closer together and collide more frequently in a certain time.
In reversible reactions, what is each collision forming a transition state called?
In reversible reactions, what is each collision forming a transition state called an Activated Complex
Given: 2NO(g) + O₂(g) ⇌ 2NO₂(g) ∆H°= -2.7 kJ/mol What will happen to the concentration of NO₂(g) for each of the following. F) lowering the temperature
Stress: Favoured: concentration of NO₂(g) goes up
For the reaction of wA + xB ⇌ yC + zD, what are the significance of the letters, w, x, y and z?
They are the coefficients
If Q < Kc, then essentially we have ____ ______ product and the reaction will proceed to the_______
If Q < Kc, then essentially we have too little product and the reaction will proceed to the right (to produce more product and decrease the concentration of reactant)
What was the results of nitroglycerin, C₃H₅N₃O₉(l) exploding? 2
Releases energy as triple bond formed Rapid increase in volume of gases (heat)
Consider the reaction: CaCO₃(s) + 2HCI(aq) ===> CaCl₂(aq) + H₂O(l) + CO₂(g). What are two ways we can graph it against time?
Decrease in concentration of HCI Using a pH meter Increase in volume of CO₂
Changing N₂(g) to a nitrogen compound is called what?
Nitrogen Fixation
Given: C₂H₅OH(l) + CH₃COOH(l) ⇌ CH₃COOC₂H₅(l) + H₂O(l) In which direction will the equilibrium shift if: D) the ethanoic acid boils away
Stress: Favoured: Direction: left/reverse
If too much ammonia is added into the soil of farmer’s fields, what develops?
Salts and it will destroy the yield of the farmer’s crops
What suddenly causes nitroglycerin, C₃H₅N₃O₉(l), to suddenly explode? 2
Being ignited Or Impacted
What does Thermodynamics show us? What can’t it show us? 2
Thermodynamics shows the energies involved in a reaction. Thermodynamics cannot show how long it takes to go to completion (or if it is ever complete!)
What are the characteristics of the reaction when K is larger than 1? 2
If K is larger than 1, the mixture contains mostly products. The reaction goes nearly to completion
Q = K No shift in reaction? Reaction will shift to the left? Reactants are greater?
Q = K No shift in reaction
What acid is processed from Contact process?
Sulfuric Acid
reaction mechanism
sequence of steps in an observable reaction
For the following equilibrium constants, predict which would exist in higher quantities — reactants or products. C) 1.09*10⁴
Products
Rate of reaction tends to ________ as reaction proceeds
Decrease
What three main things happen when the Forward reaction is favoured?
Reaction shifts towards the right side More products form Amount of reactants decreases
K is less than Q No shift in reaction? Reaction will shift to the left? Reactants are greater?
K is less than Q Reaction will shift to the left
State the conditions needed for the optimum yield of ammonia in the Haber process. Justify why these conditions are used. 4
1) High concentrations of N₂(g) and H₂(g) ➽ The ratio is always maintained at a ratio of 1:3 to make sure there is no limiting reactant and effective collisions are increased. 2) Use of catalyst - heated powdered iron oxide ➽ Heated powdered iron oxide is used because being powdered increases surface area for the reaction and being heated means that particles have more energy and collide harder, thus making sure there are a lot of effective collisions in a certain time. 3) Removal of Ammonia ➽ This drives equilibrium forward. 4) Ideal temperature is 450°C ➽ This ideal temperature is balances between high equilibrium yield and a faster reaction rate
The rate of reaction is the ____ as the slope of the curve at any moment
Same
For the reaction of wA + xB ⇌ yC + zD, how can concentrations of the reactants and products be shown? 2
By putting a square bracket around the particles [A], [B], [C] & [D]
To make Ammonia, where did Fritz Haber get the hydrogen from? 2
Methane And steam
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