Question

ction 3: adding coefficients (fix it—the legal way)
do not change subscripts you may add coefficients
directions:
balance each equation using coefficients only.

1. \underline{2} na + \underline{1} cl₂ \

ightarrow \underline{2} nacl
na = 1 \
ightarrow 2 na = 1 (changes to 2 with coefficient) \
ightarrow 2
cl = 2 cl = 1 (need 2) \
ightarrow 2

1. \underline{2} mg + \underline{1} o₂ \

ightarrow \underline{2} mgo
mg = 1 \
ightarrow 2 mg = 1 \
ightarrow 2
o = 2 o = 1 \
ightarrow 2

1. \underline{2} h₂ + \\_\\_ o₂ \

ightarrow \\_\\_ h₂o

1. \underline{4} al + \\_\\_ o₂ \

ightarrow \\_\\_ al₂o₃

1. \\_\\_ ca + \\_\\_ h₂o \

ightarrow \\_\\_ ca(oh)₂ + \\_\\_ h₂

Explanation:

Step1: Balance H₂ + O₂ → H₂O

Count initial atoms:
Reactants: $\text{H}=2$, $\text{O}=2$
Products: $\text{H}=2$, $\text{O}=1$
Add coefficient 2 to $\text{H}_2\text{O}$:
$\text{H}_2 + \text{O}_2
ightarrow 2\text{H}_2\text{O}$
Now $\text{H}=4$ on products, add coefficient 2 to $\text{H}_2$:
$2\text{H}_2 + \text{O}_2
ightarrow 2\text{H}_2\text{O}$
Verify: $\text{H}=4$, $\text{O}=2$ on both sides.

Step2: Balance Al + O₂ → Al₂O₃

Count initial atoms:
Reactants: $\text{Al}=1$, $\text{O}=2$
Products: $\text{Al}=2$, $\text{O}=3$
Add coefficient 2 to $\text{Al}$, 2 to $\text{Al}_2\text{O}_3$:
$2\text{Al} + \text{O}_2
ightarrow 2\text{Al}_2\text{O}_3$
Now $\text{Al}=4$ on products, update $\text{Al}$ coefficient to 4; $\text{O}=6$ on products, add coefficient 3 to $\text{O}_2$:
$4\text{Al} + 3\text{O}_2
ightarrow 2\text{Al}_2\text{O}_3$
Verify: $\text{Al}=4$, $\text{O}=6$ on both sides.

Step3: Balance Ca + H₂O → Ca(OH)₂ + H₂

Count initial atoms:
Reactants: $\text{Ca}=1$, $\text{H}=2$, $\text{O}=1$
Products: $\text{Ca}=1$, $\text{H}=4$, $\text{O}=2$
Add coefficient 2 to $\text{H}_2\text{O}$:
$\text{Ca} + 2\text{H}_2\text{O}
ightarrow \text{Ca(OH)}_2 + \text{H}_2$
Verify: $\text{Ca}=1$, $\text{H}=4$, $\text{O}=2$ on both sides.

Answer:

1. $2\text{H}_2 + 1\text{O}_2

ightarrow 2\text{H}_2\text{O}$

1. $4\text{Al} + 3\text{O}_2

ightarrow 2\text{Al}_2\text{O}_3$

1. $1\text{Ca} + 2\text{H}_2\text{O}

ightarrow 1\text{Ca(OH)}_2 + 1\text{H}_2$