11th NCERT Chemistry Chapter 5
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– System and Surroundings: The universe is divided into the system and surroundings. The system is the part where observations are made, while the surroundings include everything else. The system and surroundings together make up the universe. This division allows tracking of matter and energy exchanges【4:3†source】.
– Types of Systems: Systems are classified as open, closed, or isolated based on the exchange of matter and energy with the surroundings. Open systems allow both energy and matter exchange, closed systems only allow energy exchange, and isolated systems do not allow either energy or matter exchange with the surroundings【4:3†source】.
– Internal Energy, Work, and Heat: Internal energy is the sum of kinetic and potential energies of the particles in the system. Work and heat are forms of energy transfer into or out of the system. The first law of thermodynamics states that the internal energy change of a system is equal to the heat added to the system minus the work done by the system【4:3†source】.
– State Functions: Internal energy (U) and enthalpy (H) are state functions that depend only on the initial and final states, not on the path taken. Enthalpy change (∆H) can be measured experimentally and correlated with internal energy changes (∆U)【4:3†source】.
– Enthalpy Changes and Hess’s Law: Enthalpy changes for different reactions can be calculated using standard states and Hess’s law of constant heat summation. Hess’s law states that the total enthalpy change for a reaction is the same regardless of the route taken to get from reactants to products【4:3†source】.
– Spontaneity and Entropy: Spontaneous processes occur without external intervention. Entropy (S) is a measure of disorder or randomness in a system and is used to determine the spontaneity of a process. Total entropy change is positive for a spontaneous change in an isolated system【4:3†source】.
– Gibbs Energy Change: Gibbs energy change (∆G) is used to determine the spontaneity and equilibrium of a reaction. For a spontaneous change, ∆G is negative, and at equilibrium, ∆G is zero. The relationship between ∆G and spontaneity, as well as ∆G and the equilibrium constant, is established【4:3†source】.
What will be the value of ∆S for an isolated system where ∆U = 0?
For the reaction 2A + B → C at 298 K with ∆H = 400 kJ mol–1 and ∆S = 0.2 kJ K–1 mol–1, at what temperature will the reaction become spontaneous?
What are the signs of ∆H and ∆S for the reaction 2 Cl(g) → Cl2(g)?
For the reaction 2 A(g) + B(g) → 2D(g) with ∆U = –10.5 kJ and ∆S = –44.1 JK–1, calculate ∆G and predict whether the reaction may occur spontaneously.
Calculate the entropy change in surroundings when 1.00 mol of H2O(l) is formed under standard conditions.
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