By LeChatelier's principle when a <em>system</em> in <em>equilibrium</em> is disturbed, the system will react to counteract the disturbance and restore fhe equiibrium.
When one of the substances increases, look at where it appears in the chemical equilibrium equation and determine how that increase can be compensated.
In this case, the system will try to balance the increase in vapor, which is on the right side of the equation, by consuming part of it and producing more water and energy through the reverse reaction, from right to left. Thus, the system will shift left.
Isotopes are atoms of the same element that have different numbers of neutrons but the same number of protons and electrons. The difference in the number of neutrons between the various isotopes of an element means that the various isotopes have different masses.
