# Homework Help: Isotope fractionation with condensation

1. Jan 31, 2014

### Puchinita5

1. The problem statement, all variables and given/known data

I'm really confused about this concept. I know that when you evaporate a liquid, heavier isotopes stay behind because it's easier to evaporate lighter isotopes. This is intuitive to me.

I'm confused on the case of condensation because I'm reading two things that seem to contradict each other. In one source, "heavier isotopes of oxygen are selectively precipitated from an air mass as temperature decreases." This seems to be intuitive to me in the same way as evaporation. As temperature decreases, heavier isotopes would condense first.

However, in another source I'm reading, "partial condensation can produce isotopically light condensates" .... I asked my professor about this, and he says that this is because lighter elements are moving faster, so they hit surfaces more often than heavier, so they condense first. It's still intuitive to me to think that heavy isotopes have lower energy so they are just easier to slow down into the condensed state.

Am I missing something? Is there certain situations where heavy things condense first and others where lighter things condense first?

2. Relevant equations

3. The attempt at a solution

2. Jan 31, 2014

### Puchinita5

And in relation to this topic, why is it that fayalite (iron rich silicate) evaporates faster than forsterite (magnesium rich silicate) from an olivine solid solution?