Akey step in balancing chemical equations is correctly identifying the formulas of the reactants and products. for example, consider the reacti on between calcium oxide, cao(s), and h2o(l)
to form aqueous calcium hydroxide. write a balanced chemical equation for this combination reaction, having correctly identified the product as
ca(oh)2(aq).

CaO + H2O= Ca(OH)2

Explanation:

The rule of balancing chemical equation states that the total number of atoms an element on the right hand side, must equal the total number of atoms of the same element on the left hand side of the reaction equation. This rule is satisfied in the equation above. For example, there are two oxygen atoms at the RHS and two at the LHS.

as given the equation is

2al + 6 hcl > 2 alcl3 + 3 h2(g)

as per equation two moles of aluminum reacts with six moles of hcl to give two moles of alcl3 and three moles of hydrogen gas

given: three moles of al are present and 7 moles of hcl

for three moles of aluminum nine moles of hcl will be required

however as 7 moles of hcl are present so the limiting reagent is hcl

hcl is going to decide the number of moles of product formed

when six moles of hcl are present = 3 moles of h2 are formed

when one mole of hcl is present == 3/6 mole sof h2 will be formed

when 7 moles of hcl are present = 3 x 7/ 6 moles of h2 will be formed = 3.5 moles of h2