Density and molar concentration

In summary: It depends on the context in which it is used. In summary, there are two different equations for determining the mass and molar concentrations of a species, with one being specific to ideal gases and the other being more general. The correct equation to use depends on the context and the physical properties of the species being studied.
  • #1
mech-eng
828
13
Hi,all.
a book(j.p holman,heat transfer 7e,chapter 11) gives
C (subindex)A = (ro) subindex A= P subindex A x M subindex A / Ro(universal) T

but another book(stanley middleman,an introduction to mass and heat transfer) gives
Ci=(ro)i/Mi. these are very different from each other.Ci is total molar concentration of
that species and ro is density that is mass concentration to be used in Fick's law.which one is true?
 
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  • #2
mech-eng said:
Hi,all.
a book(j.p holman,heat transfer 7e,chapter 11) gives
C (subindex)A = (ro) subindex A= P subindex A x M subindex A / Ro(universal) T

but another book(stanley middleman,an introduction to mass and heat transfer) gives
Ci=(ro)i/Mi. these are very different from each other.Ci is total molar concentration of
that species and ro is density that is mass concentration to be used in Fick's law.which one is true?

The holman equation is for the mass density CA of a species in an ideal gas if the species partial pressure is PA. So ρoA is the mass density.

In the middleman equation, ρi is the mass density of species i in a liquid or a gas, and Ci is the molar density of the species.
 

1. What is density and how is it calculated?

Density is a measure of how much mass is contained in a given volume of a substance. It is calculated by dividing the mass of the substance by its volume. The equation for density is: Density = Mass / Volume.

2. How does density relate to the molar concentration of a solution?

Density and molar concentration are both measures of how much of a substance is present in a given amount of space. However, density is a measure of the mass per unit volume, while molar concentration is a measure of the number of moles of a substance per liter of solution. They are related by the following equation: Molar Concentration = Density / Molar Mass.

3. What is the difference between molarity and molality?

Molarity and molality are both units of concentration, but they differ in how they are calculated. Molarity is a measure of the number of moles of solute per liter of solution, while molality is a measure of the number of moles of solute per kilogram of solvent. Molarity is affected by changes in temperature and pressure, while molality is not.

4. How do you convert between molarity and molality?

To convert from molarity to molality, you need to know the density of the solution and the molar mass of the solute. The equation for this conversion is: Molality = Molarity x (Molar Mass / Density). To convert from molality to molarity, you need to know the density of the solution and the molar mass of the solute. The equation for this conversion is: Molarity = Molality x (Density / Molar Mass).

5. How does the concentration of a solution affect its density?

The concentration of a solution directly affects its density. As the concentration of a solution increases, the number of particles present in a given volume also increases, resulting in a higher density. Conversely, as the concentration decreases, the density also decreases. This relationship is known as the concentration-density relationship.

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