Chemistry Chapter 11: Stoichiometry Flashcards

Questions and Answers

What is the actual yield in a chemical reaction?

The amount of product actually obtained from a chemical reaction.

What is an excess reactant in a chemical reaction?

A reactant present in a greater amount than necessary.

What are stoichiometric amounts?

Quantities of reactants in the same relative amounts as those represented in the balanced chemical equation.

What is stoichiometry?

The study of quantitative relationships between the amounts of reactants used and products formed by a chemical reaction. Signup and view all the answers

What is the mole ratio in a balanced equation?

The ratio between the numbers of moles of any two substances. Signup and view all the answers

What is the excess reactant in a chemical reaction?

A reactant that remains after a chemical reaction stops. Signup and view all the answers

What is the limiting reactant in a chemical reaction?

A reactant that is totally consumed during a chemical reaction and determines the amount of product. Signup and view all the answers

What is the percent yield in a chemical reaction?

The ratio of actual yield to theoretical yield, expressed as a percentage. Signup and view all the answers

What is the theoretical yield in a chemical reaction?

The maximum amount of product that can be produced from a given amount of reactant. Signup and view all the answers

How many mole ratios can be written for a chemical reaction involving a total of n substances?

(n)(n-1) Signup and view all the answers

How to solve mole-to-mole, mole-to-mass, and mass-to-mass stoichiometric problems?

Write a balanced chemical equation, convert from grams to moles, convert from moles to moles, and convert from moles to grams. Signup and view all the answers

What is the conversion factor for mole-to-mole conversions?

moles of known x (moles of unknown/ moles of known) = moles of unknown Signup and view all the answers

How to determine the limiting reactant?

Find the number of moles of each reactant, write down the actual mole ratio, and compare it with the theoretical mole ratio. Signup and view all the answers

How to calculate the product when a reactant is limiting?

Determine which reactant is limiting, convert from grams to moles of the limiting reactant, convert from moles of the limiting reactant to moles of the product, and convert from moles of product to grams of product. Signup and view all the answers

How to calculate the amount of excess reactant left after a reaction?

Determine which reactant is limiting, convert from grams to moles of the limiting reactant, convert from moles of the limiting reactant to moles of the excess reactant, and subtract from the total amount of excess reactant. Signup and view all the answers

Why use an excess of a reactant?

Chemists often use an excess of the least expensive reactant to drive reactions to continue until all of the limiting reactant is used up. Signup and view all the answers

When would you have to look for limiting reactants?

When you are given the mass or amount in moles of both reactants. Signup and view all the answers

Why do reactions not always yield as much product as expected?

Liquid reactants and products might adhere to the surfaces of their containers or evaporate, products other than the intended ones might be formed, and some amount of solid product is usually left behind on filter paper or lost in the purification process. Signup and view all the answers

Study Notes

Stoichiometry

Stoichiometry is the study of quantitative relationships between reactants and products in a chemical reaction, based on the law of conservation of mass.

Reactants and Yield

Actual yield is the amount of product obtained from a chemical reaction, determined experimentally.
Excess reactant is a reactant present in a greater amount than necessary.
Stoichiometric amounts are quantities of reactants in the same relative amounts as those in the balanced chemical equation.

Mole Ratio and Stoichiometric Calculations

Mole ratio is the ratio between the numbers of moles of any two substances in a balanced equation.
To solve mole-to-mole, mole-to-mass, and mass-to-mass stoichiometric problems, follow these steps:
- Write a balanced chemical equation.
- Convert from mass to moles, if necessary.
- Use the mole ratio to convert from moles of the given substance to moles of the unknown substance.
- Convert from moles to mass, if necessary.

Limiting Reactant

A limiting reactant is a reactant that is totally consumed during a chemical reaction, limiting the extent of the reaction and determining the amount of product.
To determine the limiting reactant:
- Find the number of moles of each reactant.
- Compare the actual mole ratio with the theoretical mole ratio from the balanced equation.
- Determine which reactant will get used up first.

Calculating Product and Excess Reactant

To calculate the product when a reactant is limiting:
- Determine which reactant is limiting.
- Convert from grams to moles of the limiting reactant, if necessary.
- Convert from moles of the limiting reactant to moles of the product.
- Convert from moles of product to grams, if necessary.
To calculate the amount of excess reactant left after a reaction:
- Determine which reactant is limiting.
- Convert from grams to moles of the limiting reactant, if necessary.
- Convert from moles of the limiting reactant to moles of the excess reactant.
- Convert from moles to grams, if necessary.
- Subtract the amount of excess reactant that reacted from the total amount to determine how much is left over.

Excess Reactant and Reaction Yield

Chemists often use an excess of the least expensive reactant to drive reactions to continue until all of the limiting reactant is used up.
Using an excess of one reactant can also speed up a reaction.
Reactions do not always yield as much product as expected due to:
- Liquid reactants and products adhering to surfaces or evaporating.
- Formation of products other than the intended one by competing reactions.
- Solid product left behind on filter paper or lost in purification.

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Description

Review chemistry concepts related to stoichiometry, including actual yield and excess reactants, with these Chapter 11 flashcards from Chemistry Matter and Change.