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1: Kw of pure water is 10⁻¹² at 60°C. The pH of pure water at 60°C is:
a) 10⁻⁶
b) 10⁻¹²
c) 10⁻⁷
d) 10⁻⁸
✅ Correct Answer: (a) 10⁻⁶
๐๐ Short Reason
Kw = [H⁺][OH⁻] = 10⁻¹² ⇒ [H⁺] = 10⁻⁶ ⇒ pH = 6.
๐๐ง Step by Step Reasoning
Kw = [H⁺][OH⁻] = 10⁻¹²
[H⁺] = [OH⁻]= [H⁺]² = 10⁻¹² ⇒ [H⁺] = 10⁻⁶ M
pH = −log[H⁺] = −log10⁻⁶ = 6
.
๐๐ Short Reason
Kw = [H⁺][OH⁻] = 10⁻¹² ⇒ [H⁺] = 10⁻⁶ ⇒ pH = 6.
๐๐ง Step by Step Reasoning
Kw = [H⁺][OH⁻] = 10⁻¹²
[H⁺] = [OH⁻]= [H⁺]² = 10⁻¹² ⇒ [H⁺] = 10⁻⁶ M
pH = −log[H⁺] = −log10⁻⁶ = 6
.
2: H₂SO₄ is stronger acid than CH₃COOH because:
a) It gives two H⁺ ion per molecule
b) Its boiling point is high
c) Its degree of ionization is high
d) It is highly corrosive
✅ Correct Answer: (c) Its degree of ionization is high
๐๐ Short Reason
The strength of acid is measured by its degree of ionization and Kโ or pKโ values. High degree of ionization and high value of Kโ (greater than 1) or low pKโ values indicates strong acid and vice-versa..
๐๐ Short Reason
The strength of acid is measured by its degree of ionization and Kโ or pKโ values. High degree of ionization and high value of Kโ (greater than 1) or low pKโ values indicates strong acid and vice-versa..
3: Rate constant of a reaction is affected by:
a) Conc. of reactants
b) Conc. of products
c) Temperature
d) Reaction time
✅ Correct Answer: (c) Temperature
๐๐ Short Reason
Rate constant of a reaction is affected by temperature only. The rate constant depends only on temperature because it reflects the fraction of molecules with enough energy to overcome the activation barrier. Concentrations and time affect the rate, but not the constant itself.
๐๐ Short Reason
Rate constant of a reaction is affected by temperature only. The rate constant depends only on temperature because it reflects the fraction of molecules with enough energy to overcome the activation barrier. Concentrations and time affect the rate, but not the constant itself.
4: The purpose of using of catalyst in a chemical reaction is to change:
a) Equilibrium constant
b) Enthalpy of reaction
c) Nature of reaction
d) Activation energy
✅ Correct Answer: (d) Activation energy
๐๐ Short Reason
The role of a catalyst is to change the activation energy of the reaction. However, catalyst does not change Gibbs energy of reaction, enthalpy of reaction and equilibrium constant..
๐๐ง Step by Step Reasoning
๐Equilibrium constant (K) is not changed by a catalyst. It only affects the speed at which equilibrium is reached, not the position of equilibrium.
๐Enthalpy of reaction (ฮH) is a thermodynamic property and remains unchanged.
๐Nature of reaction (the overall chemical transformation) is not altered
.
๐๐ Short Reason
The role of a catalyst is to change the activation energy of the reaction. However, catalyst does not change Gibbs energy of reaction, enthalpy of reaction and equilibrium constant..
๐๐ง Step by Step Reasoning
๐Equilibrium constant (K) is not changed by a catalyst. It only affects the speed at which equilibrium is reached, not the position of equilibrium.
๐Enthalpy of reaction (ฮH) is a thermodynamic property and remains unchanged.
๐Nature of reaction (the overall chemical transformation) is not altered
.
5: Ionic reactions are classified into
a) Slow reaction
b) Fast reactions
c) Reversible reaction
d) Moderate reactions
✅ Correct Answer: (b) Fast reactions
๐๐ Short Reason
The reaction between ions is very fast. Hence ionic reactions are fast reaction.
๐๐ง Step by Step Reasoning
๐ Ionic reactions occur in aqueous solutions where ions are already present and free to move.
๐ When oppositely charged ions come close, they combine almost instantly because there is no need to break strong covalent bonds.
๐ The reaction rate is therefore very high — practically instantaneous — compared to covalent reactions
๐๐ Short Reason
The reaction between ions is very fast. Hence ionic reactions are fast reaction.
๐๐ง Step by Step Reasoning
๐ Ionic reactions occur in aqueous solutions where ions are already present and free to move.
๐ When oppositely charged ions come close, they combine almost instantly because there is no need to break strong covalent bonds.
๐ The reaction rate is therefore very high — practically instantaneous — compared to covalent reactions
6: The best alternative term for the velocity of reaction is:
a) Rate of appearance
b) Rate of disappearance
c) Average rate
d) Instantaneous rate
✅ Correct Answer: (d) Instantaneous rate
๐๐ Short Reason
Velocity of reaction is also termed as Instantaneous rate.
๐๐ง Step by Step Reasoning
๐ In chemical kinetics, the term velocity of reaction is an older synonym for rate of reaction.
๐ The rate of reaction can be expressed in two ways:
๐ Average rate → change in concentration over a finite time interval.
๐ Instantaneous rate → change in concentration at a particular instant (the slope of the tangent to the concentration vs. time curve).
๐ Since “velocity” implies the exact speed at a given moment, the best modern equivalent is the instantaneous rate.
๐ Rate of appearance/disappearance are specific to products or reactants, not the overall velocity term.
๐๐ Short Reason
Velocity of reaction is also termed as Instantaneous rate.
๐๐ง Step by Step Reasoning
๐ In chemical kinetics, the term velocity of reaction is an older synonym for rate of reaction.
๐ The rate of reaction can be expressed in two ways:
๐ Average rate → change in concentration over a finite time interval.
๐ Instantaneous rate → change in concentration at a particular instant (the slope of the tangent to the concentration vs. time curve).
๐ Since “velocity” implies the exact speed at a given moment, the best modern equivalent is the instantaneous rate.
๐ Rate of appearance/disappearance are specific to products or reactants, not the overall velocity term.