Quantitative chemistry Flashcards
Why is the law of conservation of mass?
no atoms or lost or made during a chemical reaction: mass of products=mass of reactant
What is relative formula mass of a compound?
The sum of relative atomic masses of atoms (big number)
If a reactant has appeared to change in mass, what has happened?
Reactant or product is a gas and it’s mass isn’t taken into account
Why are estimates sometimes necessary?
Because measurements come with uncertainty
What are chemical amounts measured in?
Moles - mol.
What is the mass of one mole of a substance equal to?
it’s relative formula mass
What does one mole of any substance contain?
The same number of particles, atoms, molecules or ions
Mass=
moles x relative formula mass
or
concentration x volume
Avogadros constant?
6.02 x 10^23 per mole
total moles of one elements must be…
the same on both sides of the equation
How do you use moles to balance equations?
Convert masses into grams to amounts in moles, convert number of moles to whole number ratios then know how many moles of one elements compared to another
What is a limiting reactant?
the reactant that is used up
What happens if the limited reactant is used up?
The amount of product produced is restricted to the amount of excess reactant that reacts with the limiting one
What is concentration measured in?
g/dm^3 mass per volume of solution
Percentage yield?
(amount of product produced/ maximum product possible) x 100
Why is it not possible to achieve maximum yield?
Incomplete reactions due to being reversible, some of product may be lost when separated from reaction mixture, some reactants may react in unexpected ways
How to calculate theoretical mass of a product given mass of reactant and balancing equation for reaction?
Calculate mol of reactant using mol=mass/ RFM, use balancing numbers to find mol of product, calculate theoretical mass using mass=mol x RFM
What is atom economy?
a measure of amount of starting material that ends up as useful products
How to find atom economy?
(Mr of desired product from reaction/ sum of Mr of all reactants) x 100
What are possible reasons a reaction pathway is or isn’t chosen?
atom economy, yield, rate, equilibrium, usefulness of by products
Moles=
concentration x volume
What do equal amounts of gases do?
Occupy the same volume under the same pressure and temperature
What is the volume of any gas at RTP? room temp and pressure
24 dm^3
