1. Stoichiometric Relationships Flashcards
What is kinetic energy?
Energy related to motion of an object
Solid, liquid, gas: Arrangement
Solid: Closely packed
Liquid: Also close together but less then solid
Gas: Most spread out, far apart
Solid, liquid, gas: Intermolecular forces
Solid: Strongest forces
Liquid: Weaker forces
Gas: Negligible forces
Solid, liquid, gas: Motion
Solid: Vibrate at fixed positions
Liquid: Slide past each other
Gases: Move randomly
Solid, liquid, gas: Shape
Solid: Fixed shape
Liquid: No fixed shape, takes shape of container
Gas: No fixed shape
Solid, liquid, gas: Volume
Solid: Fixed volume
Liquid: Fixed volume
Gas: No fixed volume
What are all the changes of state?
- Solid to liquid: Melting
- Liquid to gas: Evaporation
- Gas to liquid: Condensation
- Liquid to solid: Freezing
- Solid to gas: Sublimation
What is opposite of sublimation?
Deposition (gas to solid)
Why does change of state occur?
An increase in temperature = increase in average kinetic energy of molecules which allows them to overcome intermolecular forces and hence build or break bonds
Examples of sublimation
Iodine, CO2, NHCl, Mothballs, Dry ice
Difference between evaporation and boiling
- Evaporation takes place at surface and below boiling point, happens at range of temperatures
- Boiling has a specific temperature and occurs throughout the liquid
What does flat part on heating or cooling curve show and why?
It shows the melting or boiling points because when there is a change of state, the temperature remains constant
Density
Mass per unit volume (D= m/v)
Unit for density
g/cm^3 or kg/m^3
Element
Something that is made of the same kind of atom
Compound
Chemically combined substance of 2 or more different elements
Are H2 and O2 compounds?
No. They are molecules
Differences between elements and compounds
- Elements are made of one type of atom
- Elements cannot be further broken down while compounds can be chemically
- Elements are represented by a symbol instead of formulae
- Element’s properties are determined by valence electrons while compound’s properties differ from their constituent elements
- 118 known elements while compounds have endless possibilities
Mixture
2 or more substances that are not chemically combined
Difference between mixtures and compounds
- Compounds are chemically combined while mixtures are physically
- Compounds are in fixed ratio
- Compounds are pure
- Compounds have a formulae
- Properties of compounds differ but mixtures retain properties of their elements/substances
Difference between homogenous and heterogenous mixture
- Homogenous have uniform dispersion
- Homogenous have fixed ratio/composition
- Heterogenous are immiscible while homogenous do not physically separate on standing
Examples of homo and heterogenous mixtures
Homogenous: Air, honey
Heterogenous: Sand + water, oil + water
Are solutions homo or heterogenous?
Homogenous
Solute
Substance that is DISSOLVED
Solvent
Substance that DISSOLVES
Concentration
Amount of solute dissolved per unit volume of solution
Unit of concentration
g/dm^3 or mol/dm^3
Relative atomic mass
Weighted average mass of an atom compared to 1/12 mass of an atom of Carbon-12
Unit of molar mass
g/mol
Avogadro’s constant
6.02 x 10^23
What is molar mass?
Mass of one mole of a substance
How do you calculate number of moles?
Total mass/ Molar mass
Calculating mass of one molecule
Molar mass/ Avogadro constant
How do you find empirical formula?
Divide percentage by mass of element present in a mole. Find simplest whole number ratio
What is percentage composition?
Mass of element in a compound/ Molar mass of compound
How to find molecular formulae?
Divide mass by molar mass of empirical formula and multiply that into the empirical compound
What are limiting and excess reagents?
Limiting: Limit amount of product made in a chemical reaction
Excess: Reactant that remains at the end of the reaction
How do you find excess reagent?
Convert elements from mass in grams to amount in mole. Divide each amount by coefficient in balanced equation. The higher value is the one in excess
What is theoretical yield?
Maximum amount of product that can be produced assuming all reactant has reacted
How do you calculate percentage yield?
(Actual/Theoretical yield) *100
What is Avogadro’s law?
States that equal volume of gas at same temp. and pressure contain equal number of particles
What is kinetic molecular theory of gases? 5 postulates.
- Particles are in constant, random straight line motion
- Negligible forces of attraction between particles
- Collisions between particles or with surface are elastic (no energy lost)
- Distance between particles > size of particles so negligible volumes
- Kinetic energy is proportional to temperature
What is molar volume?
Volume occupied by 1 mole of gas at STP. It is 22.7 dm^3
Boyle’s Law
PV=k or pressure is indirectly proportional to volume
How do you convert Kelvin to Celsius?
K is Celsius + 273
Charles’ Law
Volume is proportional to temperature
What is the general gas equation?
P1V1/T1= P2V2/T2. Units can be any as long as they are the same
Ideal gas equation
PV= nRT where: P= Pa V= m^3 n= mol R= 8.31 J/Kmol T= K
What are the conditions of a real gas?
Occurs at high pressure and low temp.
Why is there greatest deviation from ideal gas in a real gas?
Because at low temp, they move slower and at high pressure, they are more narrowly spaced
Why are gases like helium more ideal than real?
They have low molar mass and weakest intermolecular forces
Why do NH3 and CO2 deviate greatly?
NH3 has strong H bonds while CO2 has very strong forces
Under what conditions do gases behave more like an ideal gas?
At high temperature and lower pressure. They exhibit the 5 postulates of kinetic theory
How do you calculate concentration?
Concentration= Amount of solute (mol)/volume of solution (dm^3)
OR n= CV
How do you calculate concentration for very dilute solutions?
It’s C= n/V * 10^6. Calculated in ppm (parts per million). Note: 1ppm means 1dm^3 solution has 1 mg of solute
What are standard solutions?
Solutions with precisely known concentrations
- High purity
- High molar mass
- Low reactivity
How would you calculate back titrations for finding CaCO3 in eggshells through HCl?
- Excess HCl is reacted with aq. NaOH
- Subtract acid reacted with NaOH from total acid reacted with egg shell to find mole of acid that reacted
- Calculate mass of CaCO3 by moles
- Divide mass of CaCO3 by total mass of eggshell
- Find percentage
