What are the standard math prerequisites for physical chemistry? I'm currently a chemistry major and I know that physical chemistry requires lots of calculus.  Which mathematics courses should I take so that I am well prepared for my physical chemistry courses? Specifically, I need to take courses in thermodynamics, quantum chemistry and statistical thermodynamics and beyond, as I want to specialize in physical chemistry.

Is it true that the more mathematics courses that one takes, the easier physical chemistry becomes? I'm currently taking a multivariate calculus course now, and I wonder which is the next level of math courses I should take. 

I plan to take as many mathematics courses as possible. I'm thinking of taking ordinary differential equations after i finish multivariate calculus. What additional courses beyond ordinary differential equations should I take? My school offers courses in complex analysis, real analysis, and partial differential equations. Will they be useful?
In my experience, the most helpful advanced math courses you can take for Physical Chemistry are Differential Equations and Linear Algebra. Multivariate Calculus is helpful, but not as helpful as Diff. Eq. would be, especially in the beginning. Linear Algebra is very helpful for quantum chemistry, Diff. Eq. is also helpful for quantum, but more so for statistical mechanics. In the comments you mentioned several different Diff. Eq. options - as @permeakra said, taking all of them is a good idea, but ODEs and PDEs will probably be the most useful.