Stoichiometry Flashcards
What does a balanced chemical equation tell you
A balanced chemical equation tells you what amounts of reactants to mix and what amount of a product to expect
When you know the quantity of a substance in the reaction what can you calculate
You can calculate the quantity of any other substance consumed or created in the reaction
Quantity = Amount of a substance in grams or moles
Define stoichiometry
The calculation of quantities in chemical reactions is a subject of chemistry called stoichiometry
What does stoichiometry do
Allows chemists to tally, or keep track, of the amounts of reactants and products each reaction uses and makes
What quantities can a balanced chemical equation be interpreted by
Number of atoms
Number of moles
Number of molecules
Mass
Volume
Number of atoms and an example
Number and types of atoms are not changed throughout a chemical reaction
Ex: N2 + 3H2 = 2NH3 (2 nitrogen atoms, 6 hydrogen atoms)
Number of molecules and an example
The same amount of molecules of reactants will not always make the same amount of molecules of products. This is the same for every individual reaction.
Ex: N2 + 3H3 = 3NH2 (1 nitrogen molecule, 3 hydrogen molecules, (reactants) 2 Ammonia molecules (products)
Moles and an example
Avogardo’s Number - 6.022 x 10^23 = 1 mole
The coefficients of a balanced chemical equation represent the number of moles in reactants and products
Ex: N2 + 3H2 = 2NH3 (1 mole of nitrogen, 3 moles of hydrogen, 2 moles of ammonia)
Mass and an example
A balanced chemical equation obeys the law of the conversion of mass
Mass can neither be created or destroyed but simply transferred.
Ex: N2 + 3H2 = 2NH3
Both sides are 34.08 g/mol
Volume and an example
One mole of any gas occupies a volume of 22.4 L
N2 + 3H2 = 2NH3
22.4L +3(22.4) = 2(22.4)
22.4+67.2 = 44.8 L
Volume is not conserved in this instance it takes, more to make less. Not the same on both sides
In a chemical reaction what does an insufficient quantity do
An insufficient quantity of any of the reactants will limit the amount of products that forms
Limiting reagent
The reactant that determines the amount of product that can be formed by a reaction
Excess reagent
The reactant that is not completely used up in a reaction
What is a limiter
The limiter is whichever in the smallest answer
Theoretical yield
The maximum amount of product that could be formed from given amounts of reactants.
Actual yield
The amount of product that actually forms when a reaction is carried out in the laboratory.
Percent yield: How to find
The ratio of the actual yield to the theoretical yield expressed as a percent. (Actual/theoretical (100))
Percent yield facts
1) Percent yield is a measure of the efficiency of a reaction carried out in a laboratory
2) Yields of greater than 100% are not possible
3) Actual yield is an experimental value, and can often be affected
What can you do when you know the quantity of one substance in a reaction
You can calculate the quantity of any other substance consumed or created in the reaction
Mass-to-mass calculations
1) convert the mass of the reactant or products to moles by using the molar mass ( 1mole what you have/grams of what you have)
2) Then use mole ratio to determine number of moles (coefficient and what you want/coefficient and what you have)
3) Convert back to grams by using the molar mass (Grams of what you want/1 mole of what you want)
What two things are conserved in a balanced chemical equation?
Mass and charge
What number is used to calculate mole ratios
Coefficients
