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A reaction reaches equilibrium when:
The NCERT text states: 'When the rates of the forward and reverse reactions become equal, the concentrations of the reactants and the products remain constant. This is the stage of chemical equilibrium.'
According to Le Chatelier’s principle, if a system at equilibrium is subjected to a change in concentration of a reactant, how will the system respond?
The NCERT text states under '6.8.1 Effect of Concentration Change': 'The concentration stress of an added reactant/product is relieved by net reaction in the direction that consumes the added substance.' This means the system will shift to counteract the change, i.e., consume the added substance.
Which of the following physical processes demonstrates a dynamic equilibrium?
The NCERT text uses this as an example of solid-liquid equilibrium: 'Ice and water kept in a perfectly insulated thermos flask (no exchange of heat between its contents and the surroundings) at $273 ext{K}$ and the atmospheric pressure are in equilibrium state and the system shows interesting characteristic features. We observe that the mass of ice and water do not change with time and the temperature remains constant. However, the equilibrium is not static.'
What is the primary condition for equilibrium to be possible in a physical process?
Under '6.1.5 General Characteristics of Equilibria Involving Physical Processes', point (i) states: 'Equilibrium is possible only in a closed system at a given temperature.'
In the Haber process for ammonia synthesis, experiments demonstrated that the reaction could reach equilibrium starting from different initial conditions (e.g., with $ ext{H}_2$ and $ ext{N}_2$ or with just $ ext{NH}_3$). This illustrates that equilibrium:
The NCERT text states: 'Similarly, the reaction can reach the state of equilibrium even if we start with only C and D; that is, no A and B being present initially, as the equilibrium can be reached from either direction.'
An equilibrium mixture is defined as:
The NCERT text states: 'The mixture of reactants and products in the equilibrium state is called an equilibrium mixture.'
The extent to which reactions proceed to reach chemical equilibrium can be classified into three groups. Which group describes reactions where concentrations of reactants and products are comparable at equilibrium?
The NCERT text lists three groups: '(i) The reactions that proceed nearly to completion...', '(ii) The reactions in which only small amounts of products are formed...', and '(iii) The reactions in which the concentrations of the reactants and products are comparable, when the system is in equilibrium.'
What happens to the rates of forward and reverse reactions during the approach to chemical equilibrium?
The NCERT text (Fig. 6.2 and accompanying description) explains: 'With passage of time, there is accumulation of the products C and D and depletion of the reactants A and B (Fig. 6.2). This leads to a decrease in the rate of forward reaction and an increase in the rate of the reverse reaction. Eventually, the two reactions occur at the same rate and the system reaches a state of equilibrium.'
Which of the following statements best defines a wavefront according to Huygens' Principle?
As per the NCERT text, 'A locus of points, which oscillate in phase is called a wavefront; thus a wavefront is defined as a surface of constant phase.' Option o3 directly matches this definition.
In Huygens' geometrical construction, if we know the shape of the wavefront at time $t=0$, how do we determine the shape of the wavefront at a later time $t$ for a diverging wave?
The NCERT states, 'Thus, if we wish to determine the shape of the wavefront at t = t, we draw spheres of radius vt from each point on the spherical wavefront where v represents the speed of the waves in the medium. If we now draw a common tangent to all these spheres, we obtain the new position of the wavefront at t = t.' Option o3 accurately describes this process.
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