Chemical Equilibrium and Rates Of Reaction Flashcards
Dynamic Equilibrium
Two reversible processes are occurring simultaneously at the same rate
Open System
One in which both energy and matter can be exchanged between the system and its surroundings
Closed System
One in which both energy and matter can be exchanged between the system and its surroundings
Dynamic chemical equilibrium
In a closed system, the rate if the forward reaction is equal to the rate of the reverse reaction
Common ion effect
When an ion is common in both reactions and increasing concentration of a substance disturbs equilibrium. Where there is more ions, that reac will be favoured.
yield
A measure of the amount of product obtained in a chem reaction compared to the amount of product that is possible
Equilibrium constant
-A number that shows to what extent the reactants have changed into products by the time equilibrium is established.
-Affected only by temperature
Equilibrium constant
Kc= [p] / [r]
High: pr
Heat of a reaction
The net change of chemical potential energy of the system
Exothermic reactions
Reactions which transform chemical potential energy into thermal energy
Bond formation: the stronger the bond the more energy is released when formed
Endothermic reactions
Reactions which transform chemical potential energy into chemical potential energy
Bond breaking: the stronger the bond the more energy it requires to break
Activation energy
The energy required to form the activated complex
Activated complex
A high energy, unstable, temporary transition state between reactants and the products
Reaction rate
The change in concentration per unit time of either a reactant or product
Average vs Instantaneous reaction rates
The average rate=change in concentration over a period of time. It depends on when you take the measurements. The instantaneous rate is the rate at a particular time. It is determined by finding the slope of the tangent to the concentration vs time curve at that time.
Factors that affect rate of chem reactions
- Nature of substances that react
- Surface Area of a solid
- Concentration of a solution
- Pressure of a gas
- Temperature
- Catalyst
Catalyst
A substance that increases the rate of the reaction but remains unchanged at the end of the reaction
Collision Theory
A model that explains that a reaction will only proceed when the reactant particles collide effectively. An effective collision occurs when there’s:
1. Correct Orientation:
2. Sufficient Energy: Ek>=Ea
*apply to various factor
Explain how the Nature of reacting substances affect rate of reaction?
- Gas tends to react faster than other natures of substances
- Simple aqueous ions tend ti react almost instantly
- Reactions involving ions tend to be faster than reactions involving molecules
Explain in terms of coll theory how surface area of solid affects rate of reaction?
Concept: Reactions occur on the outer layer of solids
=Surface area increases the number of coll per between reactant particles will increase
:. The no, of successful coll per unit time will increase
:. Increasing ror
This is because more particles of solid are exposed to other reactant
Explain in terms of coll theory how pressure of gas will affect ror?
GASES ONLY
Increasing the pressure brings particles closer together
:. Increasing the no. Of coll per unit time
:. Increase in successful coll per unit time
:. Increasing ror
Explain in terms of coll theory how temperature will affect ror?
temp dp Ror:
Increasing temperature increases the kinetic energy of the particles
:. More particles will have energy => Ea
:. The particles will collide more frequently
This increase the no. Of successful coll per unit time
:. Increasing reaction rate
Explain in terms or coll theory how will catalyst affect ror?
Catalyst lowers activation energy of a reaction.
:. A lower Ea means more particles will have enough to react
There will be more coll:. More successful coll per unit time
Increasing ror
Explain in terms of coll theory the relationship between reaction rate and the number of eff unit coll per u time.
Directly proportional:
Measuring Rates of Reactions: Suggest and explain each
Measuring of gas volumes:
Gas formed: Measure volume of gas-use syringe, use water to count bubbles
Precipitate: Measure turbidity per unit time of the reaction mixture
Colour change: measure time taken for colour change.
Graphs
- Maxwell Boltzmann
- Potential Energy Profile/ Enthalpy
- Conc v time
- Vol v time
- Ror v time (“normal”)
- No. Of particles v time
Reversible reaction
One in which products can be converted to reactants
Le Chat
When an external stress (change in pressure, temperature or concentration) is applied to a system in dynamic chemical equilibrium, the equilibrium point will change in such a way as to counteract that stress
Explain in terms of the rates of forward and reverse reactions the effect of the changes of pressure, temperature and concentration on the concentration/s and/or amounts of each substance in an equilibrium mixture
- Pressure
- Temperature
- Concentration
Graphs for chem reactions
Amount (no. Of moles) v time:
Concentration v time
Rate v time
Industrial processes: Chem equations, diagrams or flowcharts
Apply rate and equilibrium principles to describe how yield is affected in various industrial processes
In industrial processes conditions are chosen for their economic viability to prioritise over yield. Hence a process that has a high rate is more economically viable than a process with high yield.
Equilibrium Constant: explaination
the ratio of the equilibrium concentrations of products over the reactants each raised to the power of their stoichiometric coefficients= concentrations of a reactants and products including their stoichiometry
Industrial Process: Haber Process
F/R
Pressure
Temp
Catalyst
Endo <> Exo
Pressure: Mod-High (25-250atm)
Temp: Mod-High (400-450°C)
Catalyst: Iron Oxide
Industrial Process: Contact Process
Endo<>Exo
Pressure: Low (1-2atm)
Temp: Mod-High (400-450°C)
Catalyst: Vanadium Pentoxide V205
Industrial Process: Otswald Process
Endo<>Exo
Pressure: Low-Mod (4-10atm)
Temp: High (900°C)
Catalyst: Platinum/Rhodium
Explain in terms of coll theory how concentration affects rate of reaction?
Concentration of reactants is dp to ror:
Increasing concentration will increase the no. of particles per unit volume
This will increase the no. of coll per unit time
:. Increase the no. Of successful coll per unit time
Concentration of reactants: How to change concentration
No solids or pure liquids
Aqueous solution: Adding more solute
Gas: Adding more gas, increasing pressure
Graph question (pg13) label A,B,C,D
Answers on page
Graphs: Use of Maxwell-Boltzmann Distribution
Shows the distribution of kinetic energies
Area under graph=measure of total particles present
Increasing temperature: Ea stays the same, Graphs stretches (more particles + woder spread of mean energy)
KC constant
Written out with letters as equilibrium expression
Coefficients become exponents
Dynamic equilibrium graphs
The reaction rate versus time graph looks like a wine glass tipped on its side with the forward reaction on top and the reverse reaction at the bottom meeting way equilibrium is reached
The concentration versus time graph looks like half of a fish with his tail and body. With the reactants starting at the top and the product starting off at the bottom as constant concentrations are constant
What is the effect of catalysts
Catalyst increase the rate of the forward and reverse reaction equally
Catalyst only cause a reaction to reach equilibrium faster
Catalyst therefore have no affect on the position of the equilibrium
The harbour process
It is the combination of nitrogen and hydrogen to make ammonia
XO thermic forward reaction
Endothermic reverse reaction
Moderate to high pressure 25-250
Moderate to high temperature 400 to 450
Iron oxide catalyst
The contact process this is the manufacturing of sulphuric acid
The forward reaction is exothermic
Reverse reaction is endothermic
The pressure is love from 1 to 2
The temperature is moderate to high of 450 to 400
The catalyst is vanadium Penta oxide which is V205
The Ostwald process
manufacturing of nitric acid
The forward reaction is exothermic
The reverse reaction is endothermic
The pressure is low to moderate from 4 to 10
The temperature is high 900
The catalyst is platinum or rhodium
Energy profile exothermic
The energy of the products is less than the energy of the reactants in order to read XS energy
Energy profile endothermic
The energy of the products. More than the reactants as they need energy that is not sufficient in the reactants and therefore they take energy from the products
How do you measure the rate of the reaction when a gas is formed
If a gas is produced we can measure the volume of the gas produced using a gas syringe in a Sealed container with a cork, are use water to count the bubbles
A gas can be allowed to escape and we can measure the change in mass per unit time of the reaction mixture
Measuring the rate of reaction is when a precipitate forms
If a precipitate is formed we can measure the turbidity (the degree of cleaners) per unit time of a reaction mixture
This would be done by drawing an X at the bottom of the container and sing up until what time point the ex is no longer visible
Measuring the rate of reactions with the colour change
If a colour changes observed we can measure the time taken for the colour change to Occur 
What are different ways one can measure the rate of reaction is
Measuring the Change in the Number of moles or product per unit time
The change in concentration of reactant our product per unit time
Change in the mass of reactant our product per unit time
Change in volume per unit time
Factors that affect rate of reactions
Nate of reactant
Concentration of reactant
Temperature of reactant
Surface area of solid
Pressure of reactant
Use of a catalyst
