What effect does a rise in temperature have on the density of liquid?

Answer 1

Generally speaking liquids become less dense when heated. Higher temperature means molecules move faster and further, creating more space (void).

Apart from water, Si (silicon) is an important exception. What both have in common is a solids' structure that has plenty of empty space (they are both only 4-coordinated, diamond-structure like, contrast that with the highest possible coordination [of balls], which is 12), so when the solids melt and order breaks down, some of the empty space can be filled, hence the density of the liquids increases.

If ice was always more dense than water, we would have "permafrost" like oceans and maybe life would not have evolved at all.

The general correlation for density and temperature for fluids is :

Dt = D0(1 - Cr .delta t )

where Dt is density at t deg C;

D0 is density at 0 deg C

Cr is actual expansion coefficient of the fluid;

dela t is the change in temp. i.e.( t-o )

Answer 2

Usually a given amount of liquid will grow in volume, meaning it gets less dense. Water between 0 and 4 degrees is an exception.