Data
Volume of hydrogen gas (mL)
9 mL
Room Temperature (C)
18 C
Room Tempertare (K)
291 K
Atmospheric Pressure (torr)
7296 torr

Analysis
Write a balanced equation for the reaction between magnesium nd hydrochloric acid.
Answer: Mg(s) + HCl (aq) MgCl (aq) + H (g)

Stoichiometry
Stoichiometry is a way of describing the quantitative relationships among elements in compounds and among substances as they undergo chemical changes. if you have to calculate just about anything relating to moles or other chemical quantities, the calculations will involve stoichiometry.

The Mole A mole is simply a unit of measurement. The mass of a mole is the gram formula mass of a substance. Mole is the quantity of anything that has the same number of particles found in 12.000 grams of carbon-12. That number of particles is Avogadro's Number, which is roughly 6.02x1023. Moles give us a consistent method to convert between atoms/molecules and grams. It's simply a convenient unit to use when performing calculations.

Balancing Equations
A chemical equation describes what happens in a chemical reaction. The equation identifies the reactants and products, the formulas of the participants, the phases of the participants such as solid, liquid and gas, and the amount of each substance. To balance an equation means the chemical reaction in which the number of atoms for each element in the reaction and the total charge are the same for both the reactants and the products. In other words, the mass and the charge are balanced on both sides of the reaction. All chemical reactions must be balanced—the number of atoms, moles, and ultimately the total mass must be conserved during a chemical process. The quantities are expressed as grams or moles. To balance an equation you must follow these steps:
Determine the correct formulas for all the reactants and products in the reaction.
Begin balancing with the most complicated-looking group. A polyatomic ion that appears unchanged on both sides of the equation can be counted as a single unit.
Save the single elements reactant and products for last, especially if it is hydrogen or oxygen
If you get stuck, double the most complicated-looking group and try again.
Finally, make sure that all coefficients are in the