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