In the Gas Laws & Avogadro's Hypothesis, there were two parameters changing (variables) and two parameters being held constant. For example, in Boyle's Law, the pressure of the gas (P) varies inversely with the volume (V) of the gas while the temperature of the gas (T) and number of moles (n) are held constant.

**What would happen if three of the four parameters change while one is held constant (usually n is held constant)?**

- In this case, the Gas Laws & Avogadro's Hypothesis can not be used. Therefore, you need a new equation.

*Here is how the equation is derived.*

- P varies directly with T or P = T
- T varies directly with V or V = T
- P varies inversely with V or PV = constant
- Combining all the above and you have the following

**Combined Gas Law**(P_{1}V_{1})/T_{1}= (P_{2}V_{2})/ T_{2}(Book way to write Equ)

**The 3 different equations are a) P**_{2}= P_{1}(T_{2}/T_{1})(V_{1}/V_{2}), T_{2}= T_{1}(P_{2}/P_{1})(V_{2}/V_{1}), V_{2}= V_{1}(T_{2}/T_{1})(P_{1}/P_{2})

- Therefore, in Combined Gas Law problems, you must be given 5 of the above parameters so that you can solve the problem. The steps to solve the problem is identical to the Gas Law problems except you now have a new equation and more parameters to plug into the equation.