Molar Volume vs. Partial Molar Volume: What's the Difference?

By Janet White || Published on January 14, 2024
Molar volume is the volume occupied by one mole of a substance, whereas partial molar volume is the change in volume when an infinitesimal amount of a substance is added to a mixture.

Key Differences

Molar volume is defined as the volume occupied by one mole of a substance, typically expressed in liters per mole (L/mol). It is a characteristic of pure substances and elements. Partial molar volume, on the other hand, refers to the volume that an individual component contributes to a mixture, considering the interactions with other components.
The molar volume of a substance is a measure of how much space one mole of it occupies, which depends on its physical state and conditions like temperature and pressure. In contrast, partial molar volume is a concept used in solutions and mixtures to understand how the volume of the mixture changes with the addition of more of one component.
For a pure substance, the molar volume is constant at a given temperature and pressure. However, the partial molar volume varies depending on the composition of the mixture and the interactions between different molecules in the solution.
Molar volume is crucial in stoichiometric calculations in chemistry, particularly in the case of gases (using the ideal gas law). Partial molar volume helps in understanding the behavior of mixtures, such as in the study of solutions and colligative properties.
Molar volume is straightforward and only depends on the substance's nature and conditions, while partial molar volume requires more complex calculations, as it involves the interplay of different substances in a mixture.

Comparison Chart

Definition

Volume occupied by one mole of a substance
Volume added to a mixture by an infinitesimal amount of a substance

Context

Used for pure substances and elements
Applied to components in mixtures and solutions

Dependence

Depends on temperature, pressure, and state
Varies with mixture composition and interactions

Role in Calculations

Important in stoichiometry and gas laws
Crucial for understanding mixture behavior

Variability

Constant for a given condition
Changes with mixture composition

Molar Volume and Partial Molar Volume Definitions

Molar Volume

It's a measure of the space occupied by a mole of any substance.
He used the molar volume of the compound to determine the reaction yield.

Partial Molar Volume

It reflects the contribution of a component to the total volume of a mixture.
In the alloy, the partial molar volume of each metal was crucial for predicting its properties.

Molar Volume

Molar volume is the volume one mole of a substance occupies.
The molar volume of oxygen gas is crucial in calculating its density.

Partial Molar Volume

Partial molar volume measures volume change in a mixture per mole of added substance.
The partial molar volume indicated how the solution's volume changed with each added solute.

Molar Volume

It's a fixed value for a pure substance under specific conditions.
In her experiment, the molar volume of helium was a key variable.

Partial Molar Volume

Partial molar volume is key in studying solution properties.
She calculated the partial molar volume to understand the mixture's expansivity.

Molar Volume

Molar volume indicates the volume-mole relationship of a substance.
The molar volume of the gas was affected by changes in temperature.

Partial Molar Volume

It’s used to understand the interaction between mixture components.
The partial molar volume helped explain the anomaly in the solution's behavior.

Molar Volume

Molar volume helps in understanding the physical properties of substances.
The molar volume was used to calculate the density of the liquid.

Partial Molar Volume

Partial molar volume varies with composition in mixtures.
He observed how the partial molar volume changed with different solute concentrations.

FAQs

Does the state of matter affect molar volume?

Yes, gases, liquids, and solids have different molar volumes.

What is molar volume?

It's the volume occupied by one mole of a substance.

How is partial molar volume defined?

It's the volume change per mole of substance added to a mixture.

Where is molar volume commonly used?

In stoichiometric calculations and understanding gases.

Why is partial molar volume important in chemistry?

It helps in understanding the behavior of mixtures and solutions.

Can we measure molar volume directly?

Yes, using experimental methods and calculations.

How is molar volume used in gas laws?

It links the amount of gas to its volume under certain conditions.

What role does partial molar volume play in colligative properties?

It helps in understanding how solutes affect solution properties.

Can partial molar volume be negative?

Yes, if the addition of a substance decreases the overall volume.

Is molar volume constant for a given substance?

Yes, under specific temperature and pressure conditions.

How does mixture composition affect partial molar volume?

It changes with different ratios and interactions of components.

What factors influence partial molar volume?

The nature of solute and solvent and their interactions.

How do we calculate molar volume?

By dividing the volume by the number of moles of the substance.

Does temperature impact molar volume?

Yes, especially for gases.

Can molar volume be applied to mixtures?

It’s more applicable to pure substances.

Why is partial molar volume complex to determine?

Because it depends on the dynamic interactions in a mixture.

In what way does concentration affect partial molar volume?

It varies with changes in concentration of the components.

How does pressure influence partial molar volume?

It can affect it, especially in high-pressure mixtures.

Is partial molar volume relevant in everyday products?

Yes, in things like pharmaceuticals and food products.

What’s an example of molar volume in real life?

Determining the volume of CO2 produced in a soda can.