If a mixture of 100 . g Al and 200 . g MnO is reacted according to the reaction 2 Al(s)+3 MnO(s)

If a mixture of 100 . g Al and 200 . g MnO is reacted...

If a mixture of $100 . \mathrm{g} \mathrm{Al}$ and $200 . \mathrm{g} \mathrm{MnO}$ is reacted according to the reaction $$ 2 \mathrm{Al}(\mathrm{s})+3 \mathrm{MnO}(\mathrm{s}) \longrightarrow \mathrm{Al}_{2} \mathrm{O}_{3}(\mathrm{~s})+3 \mathrm{Mn}(\mathrm{s}) $$ which of the reactants is in excess and how many grams of it remain when the reaction is complete?

If a mixture of $100 . \mathrm{g} \mathrm{Al}$ and $200 . \mathrm{g} \mathrm{MnO}$ is reacted according to the reaction
$$
2 \mathrm{Al}(\mathrm{s})+3 \mathrm{MnO}(\mathrm{s}) \longrightarrow \mathrm{Al}_{2} \mathrm{O}_{3}(\mathrm{~s})+3 \mathrm{Mn}(\mathrm{s})
$$
which of the reactants is in excess and how many grams of it remain when the reaction is complete?

Key Concepts

Stoichiometry

Stoichiometry involves using the relationships established by a balanced chemical equation to determine the quantities of reactants needed or the amounts of products formed. This concept is key in predicting the outcome of chemical reactions by applying mole ratios derived from the balanced equation.

Balanced Chemical Equations

A balanced chemical equation represents the chemical reaction with equal numbers of atoms for each element on both sides. It provides the precise stoichiometric ratios in which reactants combine and products form, which is essential for calculating the amounts of substances involved in the reaction.

Mole Concept

The mole concept is a fundamental principle in chemistry that allows chemists to count particles by weighing substances. It provides the bridge between the microscopic world of atoms and molecules and the macroscopic amounts used in laboratory settings, enabling conversion between mass and number of particles.

Limiting Reactant

The limiting reactant is the substance in a chemical reaction that is completely consumed first, thus limiting the extent of the reaction and determining the maximum amount of product that can be formed. Identifying the limiting reactant is crucial for accurately calculating reaction yields.

Excess Reactant

An excess reactant is present in a quantity greater than necessary to completely react with the limiting reactant. After the reaction, some of the excess reactant remains unreacted, and calculating its leftover amount can be important in both practical applications and theoretical analysis.

Mass-to-Mole Conversion

Mass-to-mole conversion is a key calculation in chemistry that involves converting the mass of a substance to moles using its molar mass. This conversion is essential for applying stoichiometric relationships from the balanced chemical equation in problem-solving scenarios.

Transcript

00:01 Let's start this problem by first determining what the limiting reagent is.

00:05 To do that, let's work in moles.

00:08 First, we need to get out of grams by using the molecular weight of each one of these atoms or compounds and figuring out how many moles those are.

00:22 For aluminum, the molar mass is 26 .982 grams.

00:29 And that's for every one mole of aluminum.

00:41 Now that we're in moles of aluminum, we can use our stoichiometric ratios to figure out how much product they will make.

00:48 In this case, i'm going to use the aluminum oxide.

00:54 For every two moles, actually, of aluminum, i have one mole of aluminum oxide.

01:11 Then i can multiply and divide across, and i should get 1 .85 moles of the aluminum oxide.

01:26 Now let's compare that to the magnesium oxide.

01:33 The molecular weight of manganese oxide, if we use our periodic table, is 70 .938 grams for every one mole.

01:55 And we know for every three moles of mno, there is one mole of aluminum oxide.

02:13 Multiply this across, and we should get 0 .9 -39 moles of aluminum oxide.

02:27 So in this case, if we compare our moles of product, we see that the manganese oxide is the limiting reagent because it produces less aluminum oxide than the aluminum reagent.

02:43 And this is a great example of why it's important to work in moles and not grams, because if you look at just the grams, you'll see, oh, well, there's less aluminum than manganese oxide to start...

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