Question

thinking steps: 1. write the unbalanced chemical equation with the correct chemical formulas for reactants and products. 2. count the number of atoms of each element on both sides of the equation. 3. adjust the coefficients (whole numbers) in front of the chemical formulas to make the number of atoms of each element equal on both sides. coefficient 2h₂o subscript coefficients are used to balance equations. never change or add subscripts!
__ h₂ + o₂ → __ h₂o
__ n₂ + h₂ → __ nh₃
__ mg + hcl → mgcl₂ + __ h₂

Explanation:

Step1: Balance first equation (H₂+O₂→H₂O)

Count atoms: Reactants: 2 H, 2 O; Products: 2 H, 1 O. Multiply H₂O by 2, then H₂ by 2.
$$\ce{2H_2 + O_2 -> 2H_2O}$$

Step2: Balance second equation (N₂+H₂→NH₃)

Count atoms: Reactants: 2 N, 2 H; Products: 1 N, 3 H. Multiply NH₃ by 2, then H₂ by 3.
$$\ce{N_2 + 3H_2 -> 2NH_3}$$

Step3: Balance third equation (Mg+HCl→MgCl₂+H₂)

Count atoms: Reactants: 1 Mg, 1 H, 1 Cl; Products: 1 Mg, 2 H, 2 Cl. Multiply HCl by 2.
$$\ce{Mg + 2HCl -> MgCl_2 + H_2}$$

Answer:

1. $\boldsymbol{2}\ce{H_2} + \boldsymbol{1}\ce{O_2}

ightarrow \boldsymbol{2}\ce{H_2O}$

1. $\boldsymbol{1}\ce{N_2} + \boldsymbol{3}\ce{H_2}

ightarrow \boldsymbol{2}\ce{NH_3}$

1. $\boldsymbol{1}\ce{Mg} + \boldsymbol{2}\ce{HCl}

ightarrow \boldsymbol{1}\ce{MgCl_2} + \boldsymbol{1}\ce{H_2}$
(Note: The coefficient 1 is often omitted in chemical equations, but included here to fill the blanks as requested.)