First, we calculate the moles of ammonium nitrate: Moles = mass / molecular mass Moles = 128.4 / 80 Moles = 1.60
From the equation, it is visible that the molar ratio between ammonium nitrate and water is 1 : 2. The moles of water formed will be: 1.6 * 2 = 3.2 moles
Next, we may apply the ideal gas law equation to find the volume: PV = nRT V = nRT/P V = (3.2 * 0.082 * 314)/1.89 V = 43.6 liters