A student needs to conduct a reaction that combines chemicals a and b to synthesize product ab. if we write this as a chemical e
quation 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.)
The concept used here is the Law of Conservation of Mass. Technically, it's more specifically included in the Law of Definite Proportions. According to Dalton's atomic theory, when substances react together, they form a compound that has the same fixed ratio of the individual elements. That is the main reason why we balance, because stoichiometric coefficients are essential to obey the Law.
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.
According to the law of conservation of mass, "matter is neither created nor destroyed in the cause of a chemical reaction".
We finish with what we start with in a chemical reaction. Although new species might form, the number of atoms on both sides of the expression will still be maintained.
All chemical reactions obey this law of conservation.
Molar mass of sodium=23g 2 mole sodium gives 2 g H2 i.e 46g sodium gives 2g H2 so 65.4g will give=2.84g H2 now no. of molecules = 2.8/2*avogadros number