First, use Avogadro's law and the molar weight of oxygen to determine the number of oxygen atoms.

We know that two photons are formed from every oxygen molecule. We can use basic stoichiometry to find the number of photons generated.

It is first necessary to balance the equation.

So, sixteen moles of hydrochloric acid (HCl) would produce two moles of potassium chloride (KCl). Multiplying this ratio times two, thirty-two moles of HCl would produce four moles of KCl.

We don't know which of the reactants is limiting, so we'll need to calculate how much zinc sulfate would be produced by the given amount of each of the reactants, assuming the other is in excess. Whichever reactant would produce less zinc sulfate is the limiting reactant, and the amount of zinc sulfate produced by that reactant is the actual amount that can be produced by this mixture.

If we start with 100g of zinc, we yield 247g of zinc sulfate.

Starting with 200g of copper(II)sulfate, we yield 202g of zinc sulfate.

Less zinc sulfate can be produced by the given amount of copper(II) sulfate, so copper(II) sulfate is the limiting reactant, and 202g of zinc sulfate are actually produced by the given mixture.

In this reaction, only one element is replaced by another. NaBr becomes NaCl, with a single-replacement of chlorine for bromine. The diatomic halogens are not considered as replacing one another, as they are not bound to a cation.

A comparison of single- and double-replacements reactions is shown below.

Single-replacement:

Double-replacement:

Any combustion reaction of a hydrocarbon involves oxygen gas as a reactant, and produces carbon dioxide and water as products. In this case, two moles of hexane react with nineteen moles of oxygen to produce twelve moles of carbon dioxide and fourteen moles of water. Carbon dioxide is a gas at room temperature, and water is a liquid.

Hexane:

Reaction:

Now we can begin to balance the reaction.

Everything is balanced except oxygen; there is an odd number of oxygen to the right and an even number to the left. We can adjust this by multiplying everything by two.

The reaction of a salt, like , with an acid, like , is a double-replacement reaction. The products are a salt of the original acid (), and a second acid formed from the original salt (). Remember to keep the equation balanced.

The first step is writing, and then balancing, the chemical equation for this reaction.



From this, we are able to see that for every one mole of iron (III) nitrate that is produced, three moles of sodium bromide are produced (a 1 to 3 ratio).

The limiting reagent in this reaction is the acetyl chloride (because water is never the limiting reagent; there is always an excess of water). To solve this question, we need to convert the mass of acetyl chloride to moles. The molecular weight of acetyl chloride is:

The moles of acetyl chloride is:

The moles of hydrochloric acid produced is:

The molecular weight of  is equal to . The mass of  produced is:

The question states that the total amount of products produced is . This means that each product has  (because of 1:1 ratio). To solve this question, we need to check each answer choice to see which one matches the given information. Let’s start with the correct answer first.

Molecule A is sodium chloride and molecule B is potassium bromide. The molecular weight of sodium chloride is and the MW of potassium bromide is . The question states that we start with  of each molecule; therefore, the number of moles of each molecule is

moles of molecule A = 

moles of molecule B = 

Since it has the lower amount of moles, molecule B is the limiting reagent. We can now calculate the moles of products produced.

moles of product C = 

moles of product D = 

The calculated amounts matches with the information given in the question; therefore, molecule A is sodium chloride, molecule B is potassium bromide, and the limiting reagent is potassium bromide.

If we follow this procedure for the other answer choices we will notice that the results don’t match with the given information.

The first step is to determine the limiting reagent. To do this we need to first calculate the moles of reactants. The MW of hydrochloric acid is  and MW of cesium hydroxide is . The moles of each reactant is

Next step is to write out the balanced chemical reaction

The ratio of reactants is 1:1; therefore, since  has the smaller amount of moles it is the limiting reagent. This means that all of cesium hydroxide will be utilized in this reaction and the researcher won’t be able to salvage any cesium hydroxide. Note that there will be excess  left after completion of reaction.  of  will react with  of ; therefore, there will be a total of  of excess  .