is there any way i can figure out how to find the expansion ratio of a oxy-propane reaction????? is there an equation????????

I'm not exactly sure what you mean by expansion ratio, but you can use the ideal gas equation to get a rough estimate. Basically, you assume that the pressure of the system remains the same throughout. Then you calculate how much of each gas you have to start out with and with PV=nRT you can calculate the volume of the reactants.

 

Then using the laws of thermodynamics and the enthalpy of the reaction, you can calculate how much energy is given off by the reacting species, then determine what their change in temperature will be as a result of the energy. With this new temperature and number of moles of gases, you'll again use PV=nRT to get a rough estimate of the volume that the products of the reaction will take up.