Chapter 4 - Stoichiometry and General Concepts

Avogadro's number is based off the number of atoms in 12 grams of which element?

Pure isotope carbon-12

How many molecules are there in one mole?

6.022 x 10^23

How many hydrogen molecules are there in one mole of H2O?

12.04 x 10^23 hydrogen molecules

What is the formula for moles?

Moles = mass of sample (g)/molar mass (g/mol)

CO2 has a molar mass of 44g/mol. How many moles of CO2 do you have if you have 88g of CO2?

2 mols

What is an intrinsic property?

A property that is dependent on the identity of the substance, not the quantity of it.

What is an extrinsic property?

A property that is dependent on the quantity of the substance

Is mole considered an intrinsic or extrinsic property?

Extrinsic, as it depends on the quantity of substance being measured

What is the formula for density?

Density = mass (g)/volume (mL)

What does empirical formula refer to?

The formula that gives the lowest whole-number ratio of atoms in the compound

What is the empirical formula for glucose, C6H12O6?

CH2O

What is the formula for percent composition?

Mass of element in substance (g)/molar mass of compound (g/mol)

What is the formula for percent yield?

Percent yield = actual yield/theoretical yield x 100

What is the percent yield if an experiment has a theoretical yield of 50 grams and an actual yield of 40 g?

40/50, as such 80%

What is a mole?

mole is a SI unit for the amount of any substance

What is molar mass?

Molar mass is the sum of all atoms found in 1 mole’s worth of substance. It is expressed in grams per mole (g/mol).

What does an element’s molar mass equal to?

the element’s atomic mass

How to calculate the molar mass of a compound?

1. Find atomic mass of each element

2. Multiply atomic mass of each element by subscripts and coefficients

3. Sum up all masses and set units to g/mol

What is mole ratio?

the ratio between the amount of moles of any 2 molecules in a chemical reaction

What is the mole ratio used for?

to predict the number of products formed and the number of reactants needed

How to calculate the percent composition?

1. Find molar mass of entire compound (sum of all molar masses of elements)

2. Divide specific component’s molar mass by the molar mass of the entire compound

3. Multiply decimal by 100%

What is the molecular formula?

the molecular formula is the exact number of atoms of each element in a compound

How to calculate the molecular formula?

1. Calculate molar mass of empirical formula

2. Divide molar mass of molecular form by molecular mass of empirical form

3. Multiply each subscript by whole number from step 2

How to calculate the empirical formula from percent composition?

1. Assume 100g total sample, convert element percentage into grams

2. Divide each number of grams by element’s atomic mass

3. Divide step 2 numbers by smallest number

4. If necessary, multiply all subscripts by integer to ensure smallest whole-number ratio is obtained

What is subscripts?

the number of atoms of an element in each molecule in a chemical reaction. This number cannot be changed when balancing the chemical reaction.

When balancing a chemical reaction which number can be changed?

the coefficients

What are coefficients?

the number of each moleculein a chemical equation that indicates the relative amounts of reactants and products in a balanced reaction. It is used to balance the chemical equation and can be changed.

How to balance a chemical reaction?

1. Identify each element and quantify the reactants and products

2. Choose an element and compare the quantities

3. If needed, add coefficients to balance element

4. Repeat fo all elements until balanced

5. Check to see if whole reaction is balanced

What do we do if a coefficient is a decimal?

Multiply it out to become a whole number

What is a limiting reagent?

It is the reactant that is completely used up, which helps determine how much product is formed.

What is an excess reagent?

It is the leftover reagent that is not completely used up.

How to determine the limiting reagent?

1. Balance the chemical equation

2. Convert the given info to moles

3. Pick 1 reagent as limiting reagent.

4. Determine other reactant amount required to fully react with chosen reactant

5. If other reactant is in excess, chosen reactant is limiting reagent

6. If shortage, other reactant is limiting

What is density?

an intrinsic property that is specific to a substance. g/mL

The density of water is?

~1g/mL

If an object is denser than water, what happens?

it sinks

If an object is less dense than water, what happens?

it floats

What is theoretical yield?

the maximum number of products expected

What is actual yield?

the real quantity of product resulting from chemical reaction

What does the percent yield do?

it measures the efficiency of a chemical reaction