thermochemistry
What does “Q” in thermochemistry equal?
(mass)(specific heat capacity)(change in temp)
(m)(c)(delta T)
What was Avagandro’s gas law?
What is electronegativity?
Define enthalpy.
Enthalpy: the amount of energy within a system
Define specific heat capacity.
Specific heat capacity: the amount of heat energy required to raise 1g of a substance 1 degree Celsius
What is/are the formula/s to calculate ΔH?
ΔH = Q/n
ΔH = (energy of reactant bonds) - (energy of product bonds)
What is Pauli’s Exclusion Principle?
States that an orbital can only hold 0, 1 or 2 electrons
What is electron affinity?
Electron affinity is the change in energy caused by removing an electron. This increases up a group and across a period.
What are dispersion forces? Why do these occur?
Dispersion forces are intermolecular forces which occur due to the attraction between an electron cloud in one atom and the nucleus in another. They therefore occur in all covalent bonding.
What sub-categories can mixtures be broken into? How can these be defined?
Homogeneous mixtures: uniform, the same throughout
Heterogenous mixtures: is not uniform throughout
Compare endothermic and exothermic reactions.
Endothermic: bring energy into the system, product bonds have more energy than reactant bonds, +(delta H)
Exothermic: release energy, reactant bonds have more energy than product bonds, -(delta H)
What is Hund’s rule?
Orbitals with the same energy level are half filled before the electrons are paired up.
Compare a acids and bases. Give examples.
An acid has a pH below 7 and produces H in a aqueous solution. Properties of an acid include corrosive, sour and, typically, a rough fell. Examples of an acid include HCl, vinegar and citric acid.
A base has a pH above 7 and produces OH in an aqueous solution. Properties of a base include corrosive, bitter and feel like soap. Examples of a base include sodium bicarbonate and ammonia hydroxide.
Compare empirical and molecular formulas.
Empirical: the simplest expression of a chemical formula
Molecular: the "true" / "real" formula
How do you go from moles to particles?
multiply by 6.02 x 10 to the power of 23
When bonds break is that endothermic or exothermic? Why?
When bonds break it is exothermic. Energy is released when bonds break because the energy that exists between the atoms is released.
When bonds are made it is endothermic. Energy is used to create the bonds between atoms.
What is Aufbau’s principle?
The Aufbau principle states that electrons in the ground state fill the lowest electron orbital first.
Why is hydrogen bonding so strong?
Hydrogen bonding is simplistically, a dipole dipole bond with an extremely polar molecule. Because the two elements involved have extremely different electronegativity the opposite charges are very strong and hold molecules together the best of all intermolecular forces. This occurs with H, N, O and F specifically due to H's electronegativity being the lowest of all elements and N, O and F having the highest of all elements.
What are ideal gases and what is the ideal gas law?
Ideal gases are gases whom:
- do not loose energy when colliding with other molecules (collisions are elastic)
- the actual atom takes up no volume
- there are no intermolecular forces between the particles (no interactions)
Ideal gas law: PV=nRT
(P=pressure) (V=volume (L)) (n=moles) (R=8.13) (T=temperature)
What did Arrhenius define and what is/are the definition/s?
Bases and acids.
Bases: when in an aqueous solution produce OH
Acids: when in an aqueous solution produce H
How do you calculate specific heat capacity?
Specific heat capacity = (heat energy) / (mass x temperature change)
What are the three theories which contributed to the combined gas law and who was responsible for these theories?
Boyle's law: at constant temperature, pressure is inversely proportionate to volume (P=1/v) (P1V1=P2V2)
Charles' Law: at constant pressure, volume is proportionate to temperature (V1/T1=V2/T2)
Gay-Lussac's Law: at constant volume, pressure is proportionate to temperature (P1/T1=P2/T2)
Combined gas law: (P1V1)/T1=(P2V2)/T2
What are the special properties of water and why do they occur?
- High specific heat capacity
- high heat of vaporisation (needs a lot of water to evaporate)
- high tension surface. Occurs because cohesive (attracted to other molecules)
- adhesive (attracted to other substances)
- less dense as a solid
ALL PROPERTIES OCCUR DUE TO HYDROGEN BONDING
In an experiment a strip of copper (Cu) was placed in an aqueous solution of silver nitrate (AgNO3).
(Initial mass of copper strip = 3.78g
Final mass of copper strip = 2.11g)
If copper (II) nitrate – Cu(NO3)2 is formed during this displacement reaction calculate the mass of silver formed in the silver displacement reaction.
1. write balanced equation
2. calculate mass of Cu used, use to find moles of Cu
3. use "moles x wanted/given" to calculate moles of silver
4. use moles of silver to find mass of silver
CORRECT ANSWER: 5.67g
How is thin layer chromatography performed and how does it work?
Thin paper chromatography separates components of a mixture based on their polarity. A substance is put on the end of a polar stationary phase (paper), while the non-polar solvent slowly rises causing polar molecules within the substance to rise further up the paper, travelling with the solvent front whilst the molecules whom are the least polar stop the furthest way down and the second least polar just above them and so on and so forth.