Physical properties of pure substances

Question 1

What is a pure substance?

Answer 1

Is a substance formed only of the same type of molecules or atoms.

Examples: Gold, water, acetic acid.

Question 2

What is the boling point of a substance?

Answer 2

Is the temperature at which the vapour pressure of a liquid equals the pressure of the surroundings, the liquid undergoes a phase transition to vapour.

The higher the attraction is between the atoms or molecules of the substance, the higher the boiling point is.

Question 3

What is the melting point of a substance?

Answer 3

It is the tempreature ath which a solid undergoes a phase transition to liquid.

The higher the attraction is between atoms or molecules, the higher the melting point is.

Question 4

What is the density of a substance?

Answer 4

It is the ratio of the mass and the volume it occupies.

The SI units are kg/m³ and it is temperature dependant, substances with strong intermolecular interactions tend to have more molecules per unit volume.

Question 5

What is the equilibrium vapour pressure?

Answer 5

It is the pressure exerted by the vapour that is in equilibrium with its condensed phase, solid of liquid, at a given temperature.

The stronger the intermolecular forces are, the lower the vapour pressure is.