Answer: Rate of decomposition of acetaldehyde in a solution is 
Explanation:
Rate law says that rate of a reaction is directly proportional to the concentration of the reactants each raised to a stoichiometric coefficient determined experimentally called as order.
For a reaction : 
![Rate=k[A]^x](https://tex.z-dn.net/?f=Rate%3Dk%5BA%5D%5Ex)
k= rate constant
x = order of the reaction = 2


Thus rate of decomposition of acetaldehyde in a solution is
We can use a ratio to solve this question. Lets refer to the amount formed by the formula as a serving
1 serving needs 3/8 gal
We want to create 7/9 servings extra, so
1 + 7/9 = 16/7
1 : 3/8
16/7 : x
1/(3/8) = (16/7) / x
8 / 3 = 16x / 7
x = 7/6
He needs to use 7/6 gallons of water.