Chapter 2 - Equilibrium Flashcards
What is the difference between system and surrounding?
- Chemical Reaction = System
2. Everything else around it/ Rest of the universe = Surrounding
What is an open system?
- Most common REACTION
- Matter and energy can be exchanged with surroundings
E.g Combustion
- Cannot achieve equilibrium
What is a closed system?
a REACTION THAT Exchanges only energy but not matter with the surroundings
- Can achieve equilibrium
What are irreversible reactions? - with examples
Irreversible (non-reversible)
A reaction where the Products cannot be converted back to reactants
Such reactions will occur in one direction
E.g. Baking a cake
Combustion reaction — CH4(g) +202(g) à CO2(g) + 2H2O (g)
Once fuel is burnt, the products, carbon dioxide and water, do not react with each other under normal conditions
What are reversible reactions? with examples
Products, once formed, can react again re-forming the reactants
- Evaporation and condensation of water
- A saturated sugar solution
- Reaction of haemoglobin and oxygen gas
What does the double arrows mean in chemistry.
show an example of an equation which does this.
a double arrow is used when writing a chemical equation to show a reversible process
(water liquid to water gas)
REVERSIBILITY OF PHYSICAL AND CHEMICAL CHANGES - explain evaporation and condensation of water
REVERSIBILITY OF PHYSICAL AND CHEMICAL CHANGES
Evaporation and Condensation of water
Physical change – such as change in state can be reversed
Water can cycle between the different phases of solid, liquid and gas because each process if reversible
EVAPORATION OF WATER
H2O(L) H2O(g)
CONDENSATION OF WATER
H2O(g) H2O(L)
REVERSIBILITY OF PHYSICAL AND CHEMICAL CHANGES - explain evaporation and condensation of water in a CLOSED SYSTEM.
LOOK AT OR DRAW A DIAGRAM
The water vapour cannot escape
In general, reversible reactions in a closed system eventually reach a situation where the rates of the forward and reverse reactions are equal
At this point there will appear to be no further change to the observer
The system is described as having reached a state of equilibrium
REVERSIBILITY OF PHYSICAL AND CHEMICAL CHANGES - explain evaporation and condensation of water in a OPEN SYSTEM
LOOK AT OR DRAW A DIAGRAM
IN AN OPEN SYSTEM –
Although water can evaporate and condense, the rate of each process is NOT EQUAL
Gaseous water molecules are escaping into the atmosphere, so the rate of the reverse reaction (condensation) does not become equal to the rate of forward reaction.
Define saturated solution
Saturated solution: a solution that contains the maximum possible concentration of a solute.
REVERSIBILITY OF PHYSICAL AND CHEMICAL CHANGES - explain saturated solution of sugar in a CLOSED SYSTEM.
LOOK AT OR DRAW A DIAGRAM
A saturated solution of sugar in contact with undissolved sugar crystals at a constant temperature
The sugar molecules (C12H22O11) are dissolving at the same rate as they are crystallising and the mass of sugar crystals present is constant.
Is a REVERSIBLE process and at EQUILIBRIUM.
Equation:
C12H22O11 (s) C12H22011 (aq)
Is a CLOSED SYSTEM even though there is no lid on beaker because:
No gas is involved, therefore no loss in reactant or product molecules to the surroundings
REVERSIBILITY OF PHYSICAL AND CHEMICAL CHANGES - explain Haemoglobin and Oxygen Gas in a CLOSED SYSTEM.
When you inhale, oxygen from air combines with haemoglobin in small blood vessels in lung lining to form OXYHAEMOGLOBIN.
Equation:
Haemoglobin + oxygen ——–> oxyhaemoglobin
Is a reversible chemical reaction/
The oxyhaemoglobin transported through blood system to body cells where oxygen is released so it can be used for respiration, to provide energy for the body.
Equation:
Oxyhaemoglobin ——–> oxygen + haemoglobin
Equation therefore can also be written as:
Haemoglobin + oxygen oxyhaemoglobin
Regarded as a OPEN SYSTEM overall
Equilibrium is established in the blood as it flows through the body
During this period, it may be regarded as a CLOSED SYSTEM because there is no loss of reactants or products to surroundings.
Explain soft drink equilibrium
In a sealed bottle of Soft drink CO2 gas is in EQUILIBRIUM with dissolved CO2
CO2(g) CO2(g)
The rate at which it dissolves in the solution is equal to the rate at which it leaves the solution to form gas.
Therefore, appears to be nothing happening if viewing it
When CAP is REMOVED, the PRESSURE is REDUCED and CO2 ESCAPES into atmosphere
From CLOSED SYSTEM to now OPEN SYSTEM
NET REVERSE REACTION OCCURS, as CO2 comes out of the solution
Bubbles of gas are observed when bottle is opened
Normally happens slowly
When mentos are added to bottle of soft drink, the drink erupts violently because # The HIGH SURFACE AREA of mints provide MANY SITES to form, increasing the rate of reaction and quickly producing an eruption from the bottle.
Why do reversible reactions occur?
- When particles collide, the energy associated with collisions can break bonds in the reacting particles, allowing them to rearrange to form new products.
- Energy required to break the bonds of the reactants is known as ACTIVATION ENERGY of reaction
- Once the products form it is possible for the reverse process to occur
- If newly formed particles collide with enough energy to break their bonds (equal to the activation energy of the reverse reaction), then it is possible to re-form the original reactants
Important notes to remember about reversibility:
- IF THE FORWARD REACTION IS ENDOTHERMIC, THE REVERSE IS EXOTHERMIC, AND VICE VERSA
- REACTIONS WHERE THE ACTIVATION ENERGY FOR THE FORWARD AND REVERSE REACTIONS ARE SIMILAR, ARE LIKELY TO BE REVERSIBLE REACTION
- REVERSIBLE REACTIONS CAN REACH A POINT WHERE THE RATES OF THE FORWARD AND REVERSE REACTIONS ARE EQUAL.
- —At this point equilibrium has be achieved
Explain equilibrium in-terms of reverse and irreversible reactions:
WHEN THE RATES OF BOTH FORWARD AND REVERSE ARE THE SAME, THEN THE AMOUNTS OF REACTANTS AND PRODUCTS ARE CONSTANT.
IE. IF X is 5g, Y is 7g then X remains at 5g unless a change occurs
UNDER THESE CONDITIONS, THE NAME ATTRIBUTED IS DYNAMIC EQUILIBRIUM. NOT MASS EQUILIBRIUM.
ONLY THE SYSTEM IS BEING ACCOUNTED
Some reversible reactions can reach a point where they appear to stop. What does this mean?
— To someone observing an equilibrium system it would appear as if nothing is changing
- At this point, the CONCENTRATIONS of the REACTANTS and PRODUCTS remain CONSTANT, even though there are still reactants remaining
- Although these reactions appear to stop, they actually continue to proceed.
- . As the reactants are forming products and the products are re-forming reactants at the same rate.
Understand and explain the Habor process
- diagrams and equation
In a CLOSED SYSTEM at CONSTANT PRESSURE AND TEMPERATURE, NO further CHANGE WILL TAKE PLACE. Reaction has reached balance – an equilibrium
What does the concentration vs time graph show?
Examples and diagrams
The concentration vs. time graph shows the changes in concentrations of the chemicals with time.
When is equilibrium established?
Equilibrium is established when there is no longer any change in any concentrations.
What is partial pressure?
total pressure and what happens when increasing the amount?
It is the pressure exerted by an individual gas in a container.
- The TOTAL PRESSURE of a GAS MIXTURE is the SUM of the EFFECTS of the COLLISIONS OF ALL THE INDIVIDUAL GASES
- INCREASING the AMOUNT of the GAS in a CONTAINER of FIXED VOLUME OR REDUCING the VOLUME of the CONTAINER WILL INCREASE BOTH THE PARTIAL PRESSURE AND the CONCENTRATIONS OF the GAS.
Explain habor process affected by partial pressure;
In a vessel containing gaseous equilibrium:
N2 (g) + 3H2 (g) 2NH3 (g)
- The partial pressure of nitrogen gas is the pressure that amount of nitrogen would exert if it were only gas in the container
- Similarly, the partial pressure of the hydrogen and the partial pressure of the ammonia are the pressures these gases would exert if they were only gases in the container.
- The MOLECULES of each gas would MOVE INDEPENDENTLY AND COLLIDE WITH THE WALLS of the CONTAINER, almost as though the other gases were not there.
- The total pressure of the gaseous mixture of N, H and NH3 is the sum of their partial pressures.
- The changes that occur when Nitrogen and Hydrogen gas from an EQUILIBRIUM MIXTURE with Ammonia gas can be described by measuring the partial pressures of the individual gases.
- AT EQUILIBRIUM THE PARTIAL PRESSURES OF THE 3 GASES WILL BE CONSTANT.
What is chemical dynamic equilibrium?
CHEMICAL EQUILIBRIUM can be DESCRIBED as DYNAMIC STATE BECAUSE the FORWARD AND REVERSE REACTIONS HAVE NOT CEASED.
- Instead, they OCCUR SIMULTANEOUSLY AT THE SAME RATE
- Is REACHED by REVERSIBLE PHYSICAL OR CHEMICAL REACTIONS TAKING PLACE IN A CLOSED SYSTEM.
WHAT HAPPENS DURING DYNAMIC EQUILIBRIUM?
- MACROSCOPIC PROPERTIES are CONSTANT.
- —-Meaning any AMOUNT AND CONCENTRATIONS of REACTANTS AND PRODUCTS, the PRESSURE, AND TEMPERATURE is CONSTANT - The REACTION IS ‘INCOMPLETE’ and ALL of the SUBSTANCES (reactants and products) are PRESENT IN THE EQUILIBRIUM MIXTURE.
- AT MOLECULAR LEVEL, BONDS ARE CONSTANTLY BEING BROKEN AND NEW BONDS ARE BEING FORMED AS THE REACTANTS AND PRODUCTS CONTINUE TO BE CONVERTED FROM ONE TO ANOTHER.
