To solve the question, "The quantity which changes with temperature," we need to understand the definitions and properties of the given options: mole fraction, mass percentage, molarity, and molality.
Mole Fraction: It is the ratio of the number of moles of a component to the total number of moles of the mixture. It is a dimensionless quantity and does not depend on temperature.
Mass Percentage: It is the mass of a component divided by the total mass of the mixture, multiplied by 100. This quantity is also unaffected by changes in temperature as it is based on mass, which does not change with temperature.
Molarity (M): Molarity is defined as the number of moles of solute per liter of solution. The formula is given by: \(M = \frac{n}{V}\), where \(n\) is the number of moles, and \(V\) is the volume of solution in liters. Volume is temperature-dependent due to thermal expansion or contraction of liquids, thus molarity changes with temperature.
Molality (m): Molality is defined as the number of moles of solute per kilogram of solvent. This is expressed as: \(m = \frac{n}{m_{\text{solvent}}}\). Since mass is invariant with temperature, molality does not change with temperature.
Based on the above analysis, Molarity changes with temperature because it depends on the volume of the solution, which is temperature-dependent due to the expansion or contraction of the solvent with temperature changes.
In conclusion, the correct answer is: Molarity.
Exam Tip: Always remember that quantities involving volume (like molarity) are temperature-dependent, whereas those involving mass (like mass percentage, molality) are not.
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Molarity is defined as the number of moles of solute per liter of solution. Since the volume of a solution is affected by temperature due to thermal expansion or contraction, molarity also changes with temperature. Mass percentage, molality, and mole fraction, however, are temperature-independent as they depend only on the ratio of masses or moles of solute and solvent, which do not vary with temperature. The correct option is (c) : Molarity
Thermodynamics in physics is a branch that deals with heat, work and temperature, and their relation to energy, radiation and physical properties of matter.
Important Terms
System
A thermodynamic system is a specific portion of matter with a definite boundary on which our attention is focused. The system boundary may be real or imaginary, fixed or deformable.
There are three types of systems:
Isolated System – An isolated system cannot exchange both energy and mass with its surroundings. The universe is considered an isolated system.
Closed System – Across the boundary of the closed system, the transfer of energy takes place but the transfer of mass doesn’t take place. Refrigerators and compression of gas in the piston-cylinder assembly are examples of closed systems.
Open System – In an open system, the mass and energy both may be transferred between the system and surroundings. A steam turbine is an example of an open system.
Thermodynamic Process
A system undergoes a thermodynamic process when there is some energetic change within the system that is associated with changes in pressure, volume and internal energy.
There are four types of thermodynamic process that have their unique properties, and they are:
Adiabatic Process – A process in which no heat transfer takes place.
Isochoric Process – A thermodynamic process taking place at constant volume is known as the isochoric process.
Isobaric Process – A process in which no change in pressure occurs.
Isothermal Process – A process in which no change in temperature occurs.
Laws of Thermodynamics
Zeroth Law of Thermodynamics
The Zeroth law of thermodynamics states that if two bodies are individually in equilibrium with a separate third body, then the first two bodies are also in thermal equilibrium with each other.
First Law of Thermodynamics
The First law of thermodynamics is a version of the law of conservation of energy, adapted for thermodynamic processes, distinguishing three kinds of transfer of energy, as heat, as thermodynamic work, and as energy associated with matter transfer, and relating them to a function of a body's state, called internal energy.
Third law of thermodynamics states, regarding the properties of closed systems in thermodynamic equilibrium: The entropy of a system approaches a constant value when its temperature approaches absolute zero.
