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When heat is continuously added to a substance undergoing a phase change, what happens to its temperature?
The NCERT text clearly states, 'Note that when heat is added (or removed) during a change of state, the temperature remains constant.' This is a fundamental characteristic of phase transitions.
What is the term for the change of state from solid to vapor directly, without passing through the liquid state?
The NCERT text describes, 'The change from solid state to vapour state without passing through the liquid state is called sublimation, and the substance is said to sublime. Dry ice (solid CO2) sublimes, so also iodine.'
The latent heat of fusion (Lf) for water is $3.33 imes 10^5 ext{ J kg}^{-1}$. How much heat is required to melt 2 kg of ice at 0 °C into water at 0 °C?
The quantity of heat required for a change of state is given by $Q = mL$. Given $m = 2 ext{ kg}$ and $L_f = 3.33 imes 10^5 ext{ J kg}^{-1}$. So, $Q = 2 ext{ kg} imes 3.33 imes 10^5 ext{ J kg}^{-1} = 6.66 imes 10^5 ext{ J}$.
When 1 kg of water at 100 °C is converted into steam at 100 °C, the heat absorbed is approximately:
The NCERT text states, 'For water, the latent heat of fusion and vaporisation are $L_f = 3.33 imes 10^5 ext{ J kg}^{-1}$ and $L_v = 22.6 imes 10^5 ext{ J kg}^{-1}$, respectively. ... $22.6 imes 10^5 ext{ J}$ of heat is needed to convert 1 kg water into steam at 100 °C.' This refers to the latent heat of vaporization.
In the process of sublimation, which states of matter coexist in thermal equilibrium?
The NCERT text mentions, 'During the sublimation process both the solid and vapour states of a substance coexist in thermal equilibrium.'
The latent heat of an irreversible process like melting or boiling depends on:
The NCERT text states, 'Its SI unit is J kg–1. The value of L also depends on the pressure. Its value is usually quoted at standard atmospheric pressure.' Also, $Q = mL$, so it depends on the mass. Thus, it depends on the mass of the substance and the characteristic of the substance, which implies inherent properties and conditions like pressure.
What is the relationship between the latent heat ($L$) and the amount of heat ($Q$) required for a change of state for a mass ($m$) of a substance?
The NCERT reference clearly defines this relationship as '$Q = m L$ or $L = Q/m$ (10.13)', indicating that $Q = mL$ is the correct formula.
Consider a plot of temperature versus heat added for water at 1 atm pressure. What does a horizontal segment on this graph represent?
The NCERT text states, 'Note that when heat is added (or removed) during a change of state, the temperature remains constant.' A horizontal segment on a temperature-heat plot signifies that heat is being added without a change in temperature, which is characteristic of a phase transition.
Which of the following theories primarily addresses the energetics of covalent bond formation through orbital overlap?
The text states: 'The valence bond (VB) approach to covalent bonding is basically concerned with the energetics of covalent bond formation about which the Lewis and VSEPR models are silent. Basically the VB theory discusses bond formation in terms of overlap of orbitals.'
The formation of an $H_2$ molecule, according to Valence Bond Theory, involves the overlap of which types of orbitals?
The context mentions: 'For example the formation of the $H_2$ molecule from two hydrogen atoms involves the overlap of the 1s orbitals of the two H atoms which are singly occupied.'
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The bank mixes NEET previous year questions (PYQs) with practice questions, each tagged with its exam appearances where applicable.