Chapter 4, 5, 6, & 7 Flashcards
What does the strength of a metallic bond depend on?
- the CHARGE of the ions
- the RADIUS of the metal ion
sometimes the arrangement of the atoms is also important
does melting point increase or decrease from Al to Sn? (weird example)
it decreases due to arrangement of atoms
define alloy
homogenous mixtures of 2 or more metals, or of a metal & non-metal
when a substance more volatile?
when the attractive forces are weaker
why do longer chain alcohols become progressively less soluble in water?
due to the long hydrocarbon chains preventing hydrogen bonding b/w water molecules
What determines the melting points of ionic compounds?
- the way the particles in the crystal state are packed together
- impurities within the ionic compound
how do impurities affect ionic compounds?
they weaken the ionic compounds & result in lower melting points
why is ethanol a good solvent for substances?
because it has both polar & non-polar regions
what are negative ions sometimes known as?
they are known as acid radicals as they are formed when an acid loses one or more H+ ions
which are the strongest types of repulsions?
long-pair lone-pair repulsions are strongest due to the lone pairs being closer to the central nucleus & thus closer to the bonding electrons
what causes a polar bond?
may result from one end of the molecule being electron rich
give examples of resonance hybrids
ozone, benzene, carbonate ion, nitrate ion, & ethanoate ion
List a few allotropes of carbon
diamond, graphite, graphene, C60 fullerene
characteristics of diamond
Giant covalent
Tetrahedral
Each C is joined to 4 others
Very high melting/boiling point
Does NOT conduct electricity
HIGHEST THERMAL CONDUCTIVITY
Insoluble in water or organic solvents
NO delocalised electrons
characteristics of graphite
Giant covalent
Trigonal planar
Hexagonal ring layers held tog. by weak LDF
High melting/boiling point
Conducts electricity + good lubricant (pencils)
High thermal conductivity
Insoluble in water & polar solvents
Delocalised electrons
characteristics of graphene
Giant covalent
Trigonal planar
Single layer of hexagonally arranged C atoms
High melting / boiling point
Conducts electricity
High thermal conductivity
Insoluble in water
Delocalised electrons
C60 fullerene
Molecular
Hexagons & pentagons – looks like ball
melting/boiling point not at high as other allotropes due to molecular structure - is soft
Does NOT conduct electricity (delocalised electrons cannot move b/w molecules)
Insoluble in water but soluble in some organic solvents like benzene
Delocalised electrons
characteristics of Silicon dioxide
Giant covalent
Tetrahedral around Si, bent around O
Each Si joined to 4 O atoms, each O joined to 2 Si atoms
High melting & boiling point
Does NOT conduct electricity
Very poor thermal conductor
Insoluble in water
NO delocalised electrons
are bonds in products or reactants stronger for EXOTHERMIC reactions?
bonds in products are stronger than bonds in reactants because heat is given out to surroundings
what are standard conditions?
101 kPa, 298 K
difference b/w heat & temperature
HEAT = total energy in a given amount of substance –> depends on amount of substance present
TEMPERATURE = average kinetic energy of substance, but is independent of amount of substance present
(two substances w/ dif volume could have same temp but dif heat)
Hess’s law
the enthalpy change for a reaction depends on the difference between the enthalpy of the products & the enthalpy of the reactants - is independent of the reaction pathway
define standard enthalpy change of formation
the enthalpy change when 1 mole of the compound is formed from its elements in their STANDARD STATES at STP
what is the enthalpy change of formation of Mg in standard state?
0, since it is an element in standard form
define standard enthalpy change of combustion
enthalpy change when 1 mole of a substance is completely combusted in oxygen at STP
condition for calculating bond enthalpy
calculated in gaseous state
define average bond enthalpy
the energy needed to break 1 mole of a bond in a gaseous molecule AVERAGED over similar compounds
e.g. must be gaseous NOT diatomic (F2)
limitations of using bond enthalpies
- the energy of a particular bond will vary in dif compounds
- if more energy is required to convert gaseous water to liquid (to keep it in its standard state), this may require even more energy
significance of difference in bond enthalpies b/w ozone (resonance) & oxygen (double bond)?
it helps to protect us from the sun’s UV rays
The ozone layer protects the Earth from damaging UV radiation by absorbing both high & low energy UV light to break these bonds
Ozone absorbs lower frequency / energy than oxygen & its bond is weaker
rate of production of ozone = ?
the rate of ozone destruction
what causes holes in the ozone layer?
human-made pollutants such as CFCs & oxides of nitrogen can disrupt this process of ozone production
how can rate of reaction b/w CaCO3 & HCl be determined?
- by measuring concentration of HCl
- volume of CO2 produced
- reduction in mass
the faster a particle moves . . .
the more KINETIC energy it possesses
Collision theory
- particles must collide
- with appropriate geometry/orientation
- collide w/ sufficient energy to bring about the reaction
why does temperature result in higher reaction rates?
more of the colliding particles will possess the necessary activation energy resulting in more successful collisions
why does the rate of reactions get slower as reaction proceeds?
the reactants get used up as their concentration decreases
transition point is . . .
the point at which products can form
slower reactions tend to have . . .
HIGHER Ea values
Faster reactions tend to have . . .
LOWER Ea values
does temperature have an effect on the Ea of a reaction?
NO
what causes the increase in average kinetic energy when temperature is raised?
the very high velocity
What is dynamic equilibrium?
- concentration of products & reactants is CONSTANT
- forward & reverse reaction rates are EQUAL
example of physical equilibrium
condensation & vaporisation
requirement for equilibrium?
all reactants and products must be in SAME PHASE during equilibrium
closed system is important for equilibrium because. . .
neither matter nor energy can be lost or gained from system - MACROSCOPIC PROPERTIES ARE CONSTANT
examples of macroscopic properties
pressure, volume, temperature
What is Kc vs Qc?
Kc (constant at specific temperature) - how far a reaction proceeds
Qc - in which direction the reaction will proceed to reach equilibrium
Le Chatelier’s principle
- if a system at equilibrium is subjected to a small change, the equilibrium tends to shift so as to minimise the effect of that change
what is the value of Kc in esterification reactions?
it is 4 at 100C
if pressure is increased. . .
the position of equilibrium shifts to the side with less moles (MUST BE GASEOUS)
what happens to coloured solution if pressure is increased?
For a coloured solution, increasing the pressure will cause it to initially go a darker color until a new equilibrium is reached
effects of adding a catalyst on equilibrium
increases rate at which equilibrium is reached but has NO EFFECT ON POSITION of equilibrium (increases rate of both reverse & forward reaction equally)
When does Kc change?
ONLY WITH A CHANGE IN TEMPERATURE
effect on Kc when reaction is reversed
INVERT THE EXPRESSION (1/Kc)
effect on Kc when reaction coefficients are doubled
SQUARE THE VALUE OF Kc –> (Kc^2)
effect on Kc when reaction coefficients are halved
SQUARE ROOT THE VALUE OF Kc sqrt(Kc)
effect on Kc when 2 reactions are added together
MULTIPLE THE TWO EXPRESSIONS
Kc1 x Kc2
