When the following equation is balanced, what is the coefficient for HCl? Mg (s) + HCl (aq) → MgCl2 (aq) + H2 (g)

2

1

3

6

We have:

M

g

(

s

)

+

H

C

l

(

a

q

)

→

M

g

C

l

2

(

a

q

)

+

H

2

(

g

)

LHS

Mg = 1

H = 1

Cl = 1

RHS

Mg = 1

Cl=2

H=2

To make Cl and H have 2 on both sides, we place a 2 in front of the HCl

M

g

(

s

)

+

2

H

C

l

(

a

q

)

→

M

g

C

l

2

(

a

q

)

+

H

2

(

g

)

LHS

Mg=1, H=2, Cl=2

RHS

Mg=1, H=1, Cl=2

Thus the equation is balanced and the coefficient of Mg is 1, which is understood so it is not written in the final equation.