for this question
How many liters of H2 gas at STP are produced
when Zn reacts with 125 mL of 6.00 M HCl?
my book answers it this way:
0.125 L x 6.00 mole HCl x 1 mole H2 x 22.4 L
1 L 2 mole HCl 1 mole
= 8.40 L of H2 gas
where did the 22.4L come from?
at STP (standard temperature and pressure: T = 0 deg C , P = 1 atm), one mole of gas occupies a volume 22.4 L . or to you can derive this one using ideal gas law:
PV = nRT
where
P = 1 atm (STP)
T = 273.15 K (STP)
R = gas constant = 0.0821 L*atm/mol-K
n = 1 mol
hope this helps~ :)
The value of 22.4 L comes from the fact that 1 mole of any ideal gas at Standard Temperature and Pressure (STP) occupies a volume of 22.4 liters. In this case, the stoichiometry of the balanced chemical equation is used to convert moles of HCl to moles of H2 gas by multiplying by the appropriate mole ratios. Then, the volume of H2 gas is determined by using the conversion that 1 mole of gas occupies 22.4 liters at STP.
The value of 22.4 L comes from the fact that at standard temperature and pressure (STP), 1 mole of any ideal gas occupies a volume of 22.4 liters. This value is derived from the ideal gas law and is a standard reference value used in many gas stoichiometry calculations.
In the given question, we are trying to find the number of liters of H2 gas produced. To do this, we need to use stoichiometry to relate the amount of HCl reacted to the amount of H2 gas produced.
From the balanced chemical equation for the reaction:
Zn + 2HCl -> ZnCl2 + H2
We can see that 1 mole of Zn reacts with 2 moles of HCl to produce 1 mole of H2 gas. So, we need to convert the given volume of HCl (125 mL) to moles of HCl using its molarity (6.00 M).
Using the equation: Moles = Volume (in liters) x Molarity
Moles of HCl = 0.125 L x 6.00 M = 0.750 moles of HCl
Now, to find the moles of H2 gas produced, we use the stoichiometric ratio from the balanced equation, which is 1 mole of H2 gas for every 2 moles of HCl reacted.
Moles of H2 gas = 0.750 moles HCl x (1 mole H2 / 2 moles HCl) = 0.375 moles H2 gas
Finally, to convert the moles of H2 gas to liters at STP, we use the conversion factor of 1 mole of gas = 22.4 liters at STP.
Liters of H2 gas = 0.375 moles H2 gas x (22.4 liters / 1 mole) = 8.40 liters of H2 gas
Therefore, based on the given information and the stoichiometry of the reaction, 8.40 liters of H2 gas will be produced.