Chapter 1: Stoichiometric Relationships Flashcards
How do the 3 states of matter differ in the arrangement and movement of their constituent particles?
SOLID:
- Arrangement: Regular, fixed shape, particles are close together
- Movement: Vibrate slowly
LIQUID:
- Arrangement: Random, takes shape of container, particles are close together but further apart than solids
- Movement: Vibrate faster around each other
GAS:
- Arrangement: Random, fills container, particles far apart
- Movement: Moves fastest in all directions
What are the changes involved when there is a change in state?
HEATING CURVE:
- As time increases, the amount of kinetic energy possessed by the particles increase, causing the temperature to increase
- However, changes of state occur at a constant temperature, as heat is being supplied to overcome the intermolecular forces of attraction between particles
Distinguish between elements, atoms and compounds to explain why compounds have different properties from their constituent elements.
ELEMENT: pure substance containing only 1 type of atom
ATOM: smallest part of an element that can still be recognised as that element
COMPOUND: 2 or more elements combined chemically
- Chemical change that elements undergo to form a compound allow compounds to have different properties from their constituent elements
- Chemical equations show how elements combine in fixed ratios to form compounds (must be balanced to show conservation of mass –> same no. of atoms on both sides of equation)
Define a mixture and distinguish between homogenous and heterogenous mixtures
MIXTURE: 2 or more substances (either elements or compounds) physically mixed together
- Since components of a mixture do not undergo chemical change to form mixtures, mixtures have similar properties to their constituent elements
- And since the components are physically combined, they can also be separated using physical methods
- HOMOGENOUS MIXTURE: uniform composition, consisting only of 1 phase
- HETEROGENOUS MIXTURE: non-uniform composition and consists of more than 1 phase
Define:
- Relative atomic mass (Aᵣ)
- Relative molecular mass (Mᵣ)
- Molar mass
RELATIVE ATOMIC MASS (Aᵣ):
Average of the masses of the isotopes found in a naturally occurring sample of the element, relative to 1/12 of a carbon-12 atom
- Eg. Aᵣ of C: 12.01
RELATIVE MOLECULAR MASS (Mᵣ):
Mass of a molecule of an element/compound, relative to 1/12 of a carbon-12 atom
- Eg. Mᵣ of CO₂: 44.01
MOLAR MASS:
Mass of 1 mole of atoms in an element/compound
- Eg. Molar mass of C: 12.01 g mol⁻¹
Define 1 mole of a substance and convert between:
- No. of particles
- Avogrado’s Constant
- No. of moles
1 mole of a substance: 6.02 x 10²³ particles (Avogrado’s Constant)
No. of particles/6.02 x 10²³ = No. of mols
Convert between:
- Mass (g)
- No. of mols
- Molar mass (g mol⁻¹)
Mass (g) / No. of mols = Molar mass (g mol⁻¹)
Calculate percentage composition by mass of a substance
% composition
= (Aᵣ x no. of atoms of an element / Total Mᵣ) x 100%
Define empirical and molecular formula, and find empirical and molecular formula given mass of elements present*
EMPIRICAL FORMULA: Simplest whole number ratio of the elements in a compound
Eg. CₓHᵧ
MOLECULAR FORMULA: Total number of atoms of each element present in a molecule of the compound, and is a multiple of the empirical formula
Eg. n(CₓHᵧ)
Find empirical and molecular formula:
- Divide masses by Mᵣ to find no. of mols of each
- Express as whole number ratio (empirical formula)
- Calculate Mᵣ of compound using empirical formula
- Divide actual Mᵣ by calculated Mᵣ to find n
- Find molecular formula
Find empirical formula (combustion of hydrocarbon)
CₓHᵧ + O₂ –> x CO₂ + y/2 H₂O
- Use given masses of CO₂ and H₂O to find no. of mols of each
(x = No. of mols of CO₂)
(y = no. of mols of H₂O x 2) - Express as empirical formula
State the 2 ways of solving problems involving masses of substances
1) Conservation of mass
Total mass of reactants = Total mass of products
2) Converting to number of moles
- Use molar ratio to determine number of moles of required quantity
- Convert back to mass using formula
Calculate percentage yield
% yield
= Actual yield/Theoretical yield x 100%
Define limiting reagent and identify limiting reagent and reagent in excess
LIMITING REAGENT: reagent used up before the others
- Find no. of mols of each reactant
- Divide by coefficient in chemical equation
- Smallest number: LR
Define ideal gases, state the assumptions and state the conditions that ideal gases are best achieved at
IDEAL GAS: concept used by scientists to model the behaviour of real gases (under normal conditions, real gases behave similarly to ideal gases)
Assumptions:
- Particles themselves have no volume/volume of particles are negligible compared to the volume of the container
- Intermolecular forces of attraction between gaseous particles are negligible
Ideal conditions:
1) High temperature
- High temp: High K.E, can overcome IMFA between particles
- Low temp: Particles move slowly, making IMFA significant, and deviate from ideal behaviour
2) Low pressure
- Low pressure: Particles are further apart, making volume of particles negligible compared to volume of container
- High pressure: Particles are close together, making volume of particles and IMFA significant
State Avogrado’s law and use it to solve problems involving volumes of gases
AVOGRADO’S LAW: Equal volumes of gases measured at the same temperature and pressure have equal numbers of particles (no. of mols)
Hence,
Volume of gases ∝ Number of moles of gas
–> volumes can be used to directly compare quantities of gases (instead of converting to mole)
