1.3 Quantatative Chemistry
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40 Terms
What is the law of conservation of mass?
Mass is neither created nor destroyed in a chemical reaction
What does conservation of mass mean for equations?
They must be balanced with equal numbers of each atom on both sides
What is relative formula mass (Mr)?
The sum of the relative atomic masses of all atoms in a compound
How do you calculate Mr?
Add up all atomic masses in the formula
What does a balanced equation show about mass?
Total Mr of reactants = total Mr of products
Why might mass appear to change in a reaction?
A gas may escape or enter the system
Give an example of mass increase.
Metal reacting with oxygen forms a heavier oxide
What is uncertainty in measurements?
The range within which the true value lies
What is a mole?
A unit for amount of substance
What is the symbol for mole?
mol
What does 1 mole contain?
6.02 × 10^23 particles (Avogadro’s constant)
How is mass related to moles?
Mass = moles × molar mass
How do you calculate moles?
Moles = mass ÷ molar mass
Example: moles of 42g carbon?
42 ÷ 12 = 3.5 mol
What is molar mass?
Mass of one mole of a substance in grams
How are equations interpreted in moles?
Coefficients show mole ratios
What must be equal in a balanced equation?
Number of atoms of each element
How do you balance equations using moles?
Convert mass to moles, then simplify to whole number ratios
What is a limiting reactant?
The reactant that is completely used up
Why is the limiting reactant important?
It determines the amount of product formed
What is an excess reactant?
A reactant that is not completely used up
What is concentration (g/dm³)?
Mass of solute per volume of solution
How do you calculate mass from concentration?
Mass = concentration × volume
How does concentration change?
More solute or less volume = higher concentration
What is percentage yield?
(actual yield ÷ theoretical yield) × 100
Why is yield less than 100%?
Reaction may be reversible, product lost, or side reactions occur
What is theoretical yield?
The maximum possible amount of product
How do you calculate theoretical yield?
Use moles and balanced equation ratios
What is atom economy?
Measure of how much reactant becomes useful product
How do you calculate atom economy?
(Mr of desired product ÷ total Mr of reactants) × 100
Why is high atom economy important?
Less waste, more sustainable and economical
What is concentration in mol/dm³?
Moles of solute per volume of solution
What is the formula for concentration?
Concentration = moles ÷ volume
What is the formula linking moles, concentration and volume?
Moles = concentration × volume
How do you convert cm³ to dm³?
Divide by 1000
How do you find unknown concentration in reactions?
Use mole ratios from balanced equation
What is RTP?
Room temperature and pressure (20°C and 1 atm)
What volume does 1 mole of gas occupy at RTP?
24 dm³
How do you calculate gas volume?
Volume = moles × 24 (at RTP)
What does equal moles of gas mean?
Equal volumes at same temperature and pressure