Quantitative Chemistry Flashcards
What is relative formula mass?
The sum of relative atomic masses of all atoms in the molecular formula.
What is the equation for percentage mass of an element in a compound?
Ar x number of atoms in that element / Mr of the compound
X100
How many Avogadro particles are in one mole of a substance?
6.02 x 10^23
How much does one mole of carbon weigh?
12g
How much does one mole of nitrogen gas weigh?
2 x 14 = 28g
How much does one mole of carbon dioxide weigh?
12 + (2 x 16) = 44g
What is the formula for finding the number of moles in a given mass?
Moles = Mass/ Mr
Complete the sentence : In a chemical reaction, mass is always __________.
concerved
What is usually involved if the mass of a chemical reaction seems to change?
gas - escapes if the chemical reaction is in an unsealed reaction vessel
What does it mean if the mass of a chemical reaction increases?
One of the reactants is a gas that is found in air.
When the gas reacts to form a part of the product it becomes contained inside the reaction vessel- so the total mass increases.
What does it mean if the mass of a chemical reaction decreases?
One of the products is a gas and all reactants are solids, liquids or aqueous. Before, they are all contained in the reaction vessel but if the vessel isn’t enclosed, gas can escape causing a decrease in mass.
What are the four steps of balancing equations using reacting masses?
- Find number of moles
- Divide moles by the smallest number of moles in the equation
- If any aren’t integers, multiply them all to get whole numbers
- Write a balanced symbol equation
What happens to a reaction when a reactant is used up?
It stops.
What is the name of the reactant used up in a reaction?
the limiting reactant
What does the amount of product of a reaction depend on?
The limiting reactant
What is RTP?
Room temp and pressure
What volume does one mole of any gas occupy at room temperature and pressure?
24dm^3
What is the formula to find the volume of a known gas at RTP?
Volume = mass/Mr x24
OR
Volume = moles of gas x 24
What is concentration?
The amount of particles within a given volume.
What is the unit of concentration?
mol/dm^3
OR
g/dm^3
What is the equation to find the concentration of a solution?
Concentration = mass/ volume
How many cm^3 in 1dm^3?
1000cm^3
What is the equation for atom economy?
atom economy = Rf of desired product/ Rf of all reactants
X100
What does 100% atom economy mean?
All the atoms in the reactants have been turned into the desired product.
What is the equation for percentage yield?
percentage yield = actual mass/ theoretical mass X100
What is high atom economy better for?
profits and the environment
What are yields always less than?
100%
Why are yields always less than 100%?
- Not all reactants react
- Could be side reactions
- You lose some product when you separate it from the reaction mixture
