# Gases
+## Comibned gas equation
+
+$${P_1 V_1 \over T_1} = {P_2 V_2 \over T_2}$$
+
## Perfect gas equation
$$PV=nRT$$
-where $R =$ universal gas constant $= 8.31 \text{J} \text{K}^{-1} \text{mol}^{-1}$
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+where
+$R =$ universal gas constant $= 8.31 \text{ J K}^{-1} \text{mol}^{-1}$
+$P$ is measured in kPa
+$V$ is measured in L
+$T$ is measured in K
+$n$ is no of mol of gas
+
+
+- **Standard temperature and pressure (STP)** - standard temperature is 0 $^\circ$ C or 273 K. Standar dpressure is 100.0 kPa
+- **Standard laboratory conditions (SLC)** - temperature 25 $^\circ$ C (298K), pressure 100.0 kPa
+
+## Molar gas volume
+
+> Equal volumes of all gases measured at the same temperature and pressure contain the same number of gas particles
+
+$\therefore$ 1 mole of any gas at SLC occupies 24.8L - **molar gas volume**
+
+$$n={V \over V_M}$$
+
+where $n$ = number of mol
+$V$ = actual volume (in litres)
+$V_m$ = molar volume of gas
+
+$$\therefore n_{SLC} = {V \over 24.8}$$
+
+## Molar volume
+
+Volume of a mole of a gas - depends on pressure & temperature
+Molar gas volume = $V_M = 24.8 \text{ L mol}^{-1}$ at SLC
+Use $n = {V \over V_m}$ like $n={m \over M}$
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