Astudent needs to conduct a reaction that combines chemicals a and b to synthesize product ab. if we write this as a chemical equation it looks like: a+b→ab if this student combines 100 molecules of a and 100 molecules of b, the student obtains 100 molecules of ab. how many molecules of a would this student need to make 5000 molecules of ab? (assume the student had enough of molecule b to make 5000 molecules of ab.)
100 molecules of A would this student need to make 5000 molecules of AB.
A + B → AB
100 A molecules reacts with 100 B molecules to give 100 AB molecules.
This can also be written as , 100 molecules of AB are obtained from 100 molecules of A.
Then 5000 molecules of AB are obtained from:
molecules of A
So, in order to obtain 100 molecules of AB 100 molecules of A are needed.
For the reaction a + b ⇒ ab, this is a combination reaction. For every 1 mole of a and 1 mole of b, 1 mole of product ab is formed. This is the fixed ratio we have to follow: 1:1:1. Now, the next thing to note is the limiting and excess reactant. If initially, there are 2 moles of A and 3 moles of B, the limiting reactant is A and the excess is B. Since the ratio between reactants is 1:1, 3 moles of B requires 3 moles of A. But since only 2 moles are available, reactant A is limited. In this problem, we assume that B is provided in excess. So, we just focus on the amount of the limiting reactant a.
If there are 5,000 molecules of a, we can determine the molecules of ab using the fixed ratio, 1 part a is to 1 part ab. Then, that means that 5,000 molecules of a would yield also 5,000 molecules of ab.