Chapter 1 Flashcards
What are Irreversible reactions?
A chemical reaction in which products do not recombine to form reactants is called an irreversible reaction. Such a reaction proceeds in one direction only.
Example: When sodium reacts with water it forms sodium hydroxide and hydrogen gas.
2Na(s)+ 2H2O (l) ——-> 2NaOH (aq)+ H2(g)
The tendency of hydrogen to react with sodium hydroxide to form sodium and water is negligible at normal temperatures.
This is an example of an irreversible reaction.
Characteristics of Irreversible Reaction?
- They proceed in one direction only
- They are supposed to complete
- Products do not recombine to form reactants.
- There is no equilibrium state
- These reactions are generally fast
- They are represented by putting a single arrow between the reactants and products
Define Chemical equilibrium state.
In the case of reversible reactions, when the rate of forward reaction takes place at the rate of reverse reaction, The composition of the reaction mixture remains constant, it is called a chemical equilibrium state.
Give characteristics of a reversible reaction.
- Products recombine to form reactants.
- They proceed in both directions. i.e they consist of two reactions; forward and reverse upon conditions of reactions
- These reaction never go to completion.
How dynamic equilibrium is established?
If a reversible reaction is allowed to continue for a considerable time without changing the conditions and rates of forward and rate of reverse reactions become equal but take place in opposite directions this is called dynamic equilibrium
why at equilibrium state reaction does not stop?
It is because of the dynamic equilibrium.
The amount of reactants and products do not change in forward and reverse reactions keep on taking place at the same rate, but in opposite direction. Hence the reaction does not complete/stop
Why is the equilibrium state attainable from either way?
The concentration of species at the equilibrium stage attains the same values whether we start the reaction in the vessel in the forward direction or backward direction
What is the relationship between active mass and rate of reaction?
Active mass represents the concentration in mole dm-3 and it is expressed as a square bracket [ ]. The rate of reaction is change
in the concentration of reactant or product divided by the time taken to the change.
It is expressed as R = Δc/Δt. So, when the active mass of a substance changes its rate also changes.
How can you know that a reaction has achieved an equilibrium state?
If the value of forward becomes equal to reverse then, the reaction is said to be in equilibrium state such reaction has comparable amounts of reactants and products at the equilibrium position. Another indication is free energy changes to zero.
What are the characteristics of a reaction that establishes an equilibrium state once?
There are the following important characteristics of such a reaction:
- The reaction is reversible.
- The rates of forward and reverse reactions become equal.
- Amounts of reactants and products remain the same.
- It can be disturbed and achieved again under specific conditions.
An Industry was established based on reversible reactions. It failed to achieve products on a commercial scale. Can you point out the basic failure being a chemist?
There are following certain reasons for the failure of the chemical industry.
- Reaction is reversible so, products recombine to form reactants and dynamic equilibrium is established, we cannot get more products for sale.
- Reaction conditions like temperature, pressure and catalyst are not satisfied.
Which process is responsible for the existence of life on the earth?
We and all other living organisms owe existence to the equilibrium phenomenon taking place in the atmosphere. e.g. We inhale oxygen and exhale Carbon dioxide, while plants consume carbon dioxide and release oxygen. This natural process is responsible for the existence of life on the earth.
What is a chemical reaction?
When one or more than two substances
after a certain chemical change is converted into some new substances; which is entirely different from the original substances, we say a chemical has occurred.
What is the difference between product and reactant?
Reactant:
In a chemical reaction, the substances that combine are called reactants.
Product:
In a chemical reaction, the new substances formed are called products
Explanation:
Consider the following general reaction
A+B -------> C+D
Where A and B are reactants while C and D are products. C and D have entirely different chemical characteristics from those of A and B.
Define reversible.
Reversible reaction:
Reversible reactions are those in which products recombine to form reactants. They
proceed in both directions I.e. forward and reverse directions.
Example:
2HI (g) -----∆-----> H2 (g) + I2 (g)
colourless colour purple
product reactants
Complete the equations:
CaCO3 <———> _______?
H2 ++ I2 <———> _______?
CaCO3 <———> CaO CO2
H2 + I2 <———> 2HI
Define forward reaction.
In a reversible reaction, the reaction which goes from left to right is called forward reaction.
Example:
Consider the reversible chemical reaction
between hydrogen and Iodine. Iodine(I2) is purple. when hydrogen and Iodine vapours are heated in a closed flask as a result colourless hydrogen iodide is formed. This reaction is called forward reaction.
H2 (g) + I2 (g) -----∆-----> 2HI (g)
What is the difference between forward and reverse reaction?
Forward Reaction:
- It is a reaction in which reactants react to form products
- it goes from left to right,
- At the initial state, the rate of forward reaction is very fast.
- it slows down gradually.
Reverse reaction:
- It is a reaction in which products react to form reactants
- It goes from right to left.
- At the initial state, the rate of the forward reaction is negligible.
- Its rate gradually increases.
Write two possibilities of a chemical equilibrium state.
- Static equilibrium.
- Dynamic equilibrium.
What is meant by dynamic equilibrium?
The dynamic equilibrium state is one at which forward and reverse reactions proceed at an equal rate but in opposite directions. So, that overall reaction does not stop.
Give two microscopic characteristics of dynamic equilibrium.
- Dynamic equilibrium is only attainable in a closed container (In which substances can nether leave not enter)
- At equilibrium state reaction does not stop. Forward and reverse reactions keep taking place at the same rate but in opposite directions.
Which type of reaction does not go to completion?
Reversible reactions do not go to completion. They achieve dynamic equilibrium where by reaction keeps taking place without any change in reaction.
Why do reversible reactions never complete?
Because products recombine to form reactants and reactions occur in both directions i.e. forward and backwards. Reaction having a small magnitude of Kc represents the establishment of an equilibrium state.
What is a static equilibrium state? Explain with an example.
Static Equilibrium:
When the reaction ceases to proceed, it is called static equilibrium.
Example:
Static equilibrium is mostly observed in physical phenomena. for example, a building remains standing rather than falling down because all the forces acting on it are balanced. this an example of static equilibrium
Define active mass and give it units.
Active mass: The term “active mass” represents the concentration in mole dm-3
of reactants and the products for the dilute solution, expressed as square brackets [ ].
Define the Law of Mass Action.
The rate at which a substance reacts is directly proportional to its active mass and the rate of reaction is directly proportional to the product of the active masses of the reacting substances.
How active mass is represented?
Active mass is represented in square brackets [ ].
What is the chemical equilibrium constant?
How it is represented.
The ratio of the product of the concentration of products raised to the power of co-efficient to the product of the concentration of reactants raised to the power of co-efficient as expressed in a balance chemical equation is called the equibroim constant.
Mathematically; Kc = Product of concentration of products raised to the power of coefficients / Product of concentration of reactants raised to the power of coefficients
In which direction reaction will proceed if Qc < Kc.
If Qc < Kc, the reaction goes from left to right. So, the reaction will proceed in forward direction.
What is meant by the extent of a reaction?
The extent of the reaction measures how far a reaction proceeds before establishing an equilibrium state. It indicates to which extent reactants are converted into products. So, numerical values of the equilibrium constant (Kc) predict the extent of a reaction. There are three possibilities to predict the extent of a chemical reaction.
