Stoichiometry Flashcards
What does chemistry explain?
Chemistry explains everything you can see. How it looks, how it feels, the way it behaves the way it does by describing everything that you can’t see
What does chemistry help us understand?
Chemistry helps us understand the biggest stuff in the universe by helping us understand the tiniest
In regards to the chemical scale how big are we?
On a chemical scale we are huge. Literally massive
What is stoichiometry?
The science of measuring chemicals that go into, and come out of, any given reaction In Greek it means “Measuring Elements” It allows us to count atoms and molecules by weighing them
What is Relative Atomic Mass?
Relative Atomic Mass is the average atomic mass of all the naturally occurring isotopes of that element
For example all Carbon occurs as one of 3 isotopes
12C 13C 14C all have 6 protons but number of neutrons varies
The relative atomic mass of Carbon is weighted average of these 3 masses which comes out as 12.01amu
What are amu?
Atomic Mass Units.
The value for a single amu is 1/12 of the mass of an atom of 12C
How was amu decided upon as a universal form of measurement?
Until the 1800s chemists around around the world used different yard sticks for measuring aroms. Most commonly used was Hydrogen atom and Oxygen atom. In 1912 Isotopes were discovered ruining many scientists methods for weighing atoms. 50 years later everyone agreed to use carbon 12 as it is common
AMU has been used universally since 1961
What is a mol?
Moles are arguably the most important unit in chemistry as they allow us to express a chemical’s relative atomic mass in terms of grams
Moles
6.022x1023 = number of atoms in 12 grams of 12C
This is known as Avogadro’s Number named in his honour
How many atoms in a mol?
A mole of any element contains
6.022x1023 atoms of that element no matter what
This allows us to express elements in grams allowing us to weigh the atoms
1 mole of 12C = 6.022x1023atoms (12 grams)
1 mole of 8O = 6.022x1023 atoms (16 grams)
8O=16amu
How do molar mass (M) and relative atomic mass compare(RAM)?
Molar Mass (M) in grams = Relative Atomic Mass (RAM) in amu
The muber of atoms per mole remains the same but the mass of a mole depends on the average mass of the element
1H 1 mol H = 1.008g
26Fe 1 mol Fe = 55.85g
6C 1 mol C = 12.01g
What is the chemical formula for Sucrose?
C12H22O11
How many mols of each element does sucrose contain?
Sucrose = C12H22O11
12 mols Carbon
22 mols Hydrogen
11 mols Oxygen
What is the mass of 1 mol of sucrose?
Sucrose = C12H22O11
Carbon > 12 mol x 12.01g/mol = 144.12g
Hydrogen > 22 mol x 1.008g/mol = 22.176g
Oxygen > 11 mol x 16.00g/mol = 171g
Mass of 1 mol sucrose = 342.296g
Why does this equation not reflect chemical reality?
C12H22O11 + O2 = CO2 + H2O
Reactants ^^ ^^Prodcuts
During a reaction bonds are broken and new ones are formed but THE NUMBER OF ATOMS OF EACH ELEMENT REMAINS THE SAME
CONSERVATION OF MASS YO!
Reconciling the reactants with the products is called Equation Balancing
How can the equation become a balanced equation?
C12H22O11 + O2 = CO2 + H2O
Reactants ^^ ^^Prodcuts
Start with the most complicated mlecule in this case Carbon
C12 Right off the bat you know you’ll have to end up with at least 12 molecules of CO2 as this is the only place the carbon ends up
Next the Hydrogen
H22 We start with 22 molecules of Hydrogen
There are 2 Hydrogen atoms in water molecule H2O
So at least 11 water molecules 11 H2O
Finally Oxygen
Since we know we have:
12 CO2 molecules = 24 O Atoms
11 H2O molecules = 11 O Atoms
total = 35 Atoms
C12H22O11 + O2 = 12CO2 + 11 H2O
35 O Atoms - 11 O Atoms (from H2O)
= 24 O Atoms (missing from equation)
C12H22O11 + 12 O2 = 12 CO2 + 11 H2O
Conservation of Mass YO!
