Answer: The coefficient is 2
Step-by-step explanation:
What are coefficients?: They tell how many molecules of a substance are in a reaction
When trying to balance an equation, it helps to write down the coefficients given in the original equation. *subscripts also contribute to the molecule count, so Cl₃ will have 3 as its coefficient in the table*
In the original equation:
Reactants Products
Al 1 1
H 1 2
Cl 1 3
Now that you have your table written out, begin balancing the equation by changing the coefficients of one of the elements. For example, change the 1 in the hydrogen on the reactant side to a 2 to match the coefficient of the hydrogen on the product side.
Be mindful! Changing the 1 to a 2 also changes the 1 in chorine to a 2, since hydrogen and chlorine are connected on the reactant side as HCl.
Now, change your table to match this information:
Reactants Products
Al 1 1
H 2 2
Cl 2 3
Now, match the Cl from the reactant side to the Cl on the product side. By using the Common Factor rule, you can multiply Reactant Cl's coefficient by 3 to get 6 and Product Cl's coefficient by 2 to get 6. Once again, pay attention to the elements that might be attached to the chlorines!
Reactant Cl is attached to hydrogen, so the coefficient in front of hydrogen also changes to 6. Product Cl is attached to an aluminum, so that coefficient changes to 2.
This is what your table should look like now:
Reactants Products
Al 1 2
H 6 2
Cl 6 6
The final step of this process becomes easier, as H₂ and Al are isolated elements in this reaction. Add a 3 in front of H₂ to end up with 6 that will match the 6 on the reactant side (3 × 2 =6). Add a 2 in front of Reactant Al to match the 2 on Product Al.
Reactants Products
Al 2 2
H 6 6
Cl 6 6
Your equation should now look like this:
2Al + 6HCl→ 2AlCL₃ +3H₂
The coefficient of aluminum is 2