Chem: Thermochemistry 3.4

Total Entropy change

Sys + surr

What form has the least entropy

Solid

What form has the most entropy

Gas

Change in entropy when solid melts

Entropy increases

Change in entropy when liquid freezes

Entropy decreases

Change in entropy when liquid boils to form gas

Entropy Increases

Change in entropy when gas condenses to form liquid

Entropy decreases

Change in entropy when temperature increases

Entropy Increases

Change in entropy in number of moles increases

Entropy increases

Why does entropy increase when temperature does

Particles have more energy

Why does entropy increase when number of moles does

more particles means more possible arrangements so disorder increases

When the products have less energy than the reactants it is

Exothermic

When the products have more energy than reactants it is

Endothermic

Most spontaneous reactions are

Exothermic

Why may some spontaneous reactions be Endothermic

Entropy

A reaction that is exothermic and has an increase in entropy  will

Always be spontaneous

A reaction that is endothermic and has a decrease in entropy will

Never be spontaneous

What formula can be used when solving for enthalpy of a reaction

Sum of change in products - sum of change in reactants

What is ∆cH°(H₂(g)) same as

∆fH°(H₂O (l))

What is ∆cH° (C(s)) the same as

∆fH° (CO₂ (g))

What is  ∆cH° ( S (s)) the same as

∆fH° (SO₂ (g))

When calculating change in entropy, when do the molecules cancel out

When they are on opposite sides of the reaction

When does entropy increase

when there is a greater dispersal of matter and energy

q is in kJ so…

It needs to be in J so x by 1000

Why might temp change of water be a source of error when calculating enthalpy?

Heat from beaker lost to surrounding due it being poorly insulated and heat being lost to the gauze. Therefore, less heat id transferred to the water than should be.

Why may an enthalpy value be more exothermic than the experiment shows? (2 reasons)

Beaker not insulated so more head escapes and therefore less heat is transferred to the liquid, and some incomplete combustion occurred therefore less heat energy is released than a complete combustion. 

When do electrons increase in energy

When they are found further from the nucleus

When are subshells stable and not stable

Full and half-filled subshells are more stable than partially filled subshells.

What orbitals does energy level one contain

1s

How many electrons can fit into the S orbital

2

How many orbitals are in the 2nd energy level

s and p

How many electrons can fit into the p orbital

6

What orbitals are in the 3rd energy level

s, p, and d

How many electrons can fit into the d orbital

10

What shell must be filled before 3d

4s

What orbitals are in the 4th energy level

s, p, d, and f

What atoms have unusual electron configurations?

Copper and Chromium

When transition metals (Like iron) form ions, what electrons are lost first

4s electrons

What is an oxidation state?

A description of how many electrons it has lost or gained from its original state

What causes an increase in oxidation number

oxidation

What causes a decrease in oxidation number

Reduction

What makes good oxidising agents?

Ions in higher oxidation states

What become reducing agents

Elements in low oxidation states

When does Atomic radius increase

Going DOWN a group

Why does the atomic radius increase when you go down a group

Valence electrons are added to an energy level further from the nucleus with increased repulsion/ shielding from inner shells. Although the number of protons increases down a group, this attraction is offset by the increasing distance between the nucleus and the valence electrons. So, the electrostatic attraction between the positive nucleus and its valence electrons decreases, making the atomic radius increase as you go down a group

When does atomic radius decrease

Going across the row of the periodic table

Why does atomic radius decrease as you do across a period

Although the valence electrons are in the same energy level with the same repulsion / shielding from inner shells, the number of protons increases across a period. So, the electrostatic attraction between the positive nucleus and its valence electrons increases, and therefore the atomic radius decreases

Define “First ionisation energy”

Energy required to remove the outermost electron from one mole of gaseous atoms

When does ionisation energy decrease

When you go down a group

Why does ionisation energy decrease as you go down a group?

Ionisation energy decreases down a group because the valence electron to be removed is in an energy level further from the nucleus with greater repulsion / shielding from inner energy levels. Although the number of protons increases down a group, this effect is offset by the increasing distance between the nucleus and the valence electron to be removed. This means the electrostatic attraction between the positive nucleus and the valence electrons decreases down a group

When does ionisation energy increase

Across a period

Why does ionisation energy increase across a period of the periodic table

Although the valence electrons are in the same energy level with the same repulsion / shielding from inner shells, the number of protons increases across a period. So, the electrostatic attraction between the positive nucleus and the valence electrons increases, and therefore more energy is required to remove the outermost electron, which is why ionisation energy increases across a period

Define “Electronegativity”

A measure of the tendency of an atom to attract a bonding pair of electrons

When does electronegativity increase

It increases across a period

Why does electronegativity increase across a period

Nuclear charge increases while shielding remains the same causing increasing attraction to the nucleus

When does electronegativity decrease

Down a group

Why does electronegativity decrease down a group

While nuclear charge and shielding both increase, electron shells are added so the radius increases causing a decreasing attraction of electrons to the nucleus

Why is the radius for a non-metal ion greater than its non-metal atom?

As it gains electrons to form an ion,there is increased electron-electron repulsion in the valence energy level while nuclear charge / number of protons remains the same. This causes the valence electrons to move further away from the nucleus, making the non-metal ion have a larger radius than the non-metal atom

Why do metal ions have a smaller radius than its atom

It loses electrons and the ion has one less energy level than its atom. Therefore while the have the same number of protons, the ion is attracting less electrons, so it has a smaller radius

When is a bond polar in terms of difference in electronegativity?

When the difference is less than 1.6

Why do molecules with large molar masses have stronger TDD

Because they contain more electrons and have a larger electron cloud which results in a more uneven distribution of electrons being possible and stronger temporary dipoles forming. A larger electron cloud provides more area for attractions to form. As a result, larger molecules are more easily polarised and therefore will from stronger TDD

What type of attraction is in a non-polar molecule?

TDD

What Type of attractions are in polar molecules 

TDD and PDD

What type of attractions are in polar molecules that contain an H-atom bonded to a N, O, or F atom?

TDD, PDD, and H-Bonding

What atoms must an H atom be bonded to in order to have hydrogen bonding?

N, O, or F

If the molecules given all have a similar molar mass but different vap/boiling points you..

Molar masses similar so TDD strength is too, all molecules have TD, polar molecules have TD and PD, mention if they have hydrogen bonding. Since TD strength is similar, the difference in vap/boiling points is due to the strength of PD and/or H-bonding which is due to intermolecular forces requiring more energy to break intermolecular forces between molecules.

If the molecules have similar vap/boiling points but different molar masses you.. 

Molar masses different so TD strength in larger molecules is greater, all have TD, polar have TD and PD, mention H-bonding, since TD strength is greater between one of the given molecules this could compensate for the stronger PD or H-bond present in the other molecules given, link to strength of intermolecular forces requiring more energy to break intermolecular forces between molecules and hight vap/ boiling points. 

5 bonded pairs 0 lone pairs

Trigonal Bipyramid, 90° and 120°

4 bonded pairs, 1 lone pair

See-saw, 90° and 120°

3 bonded pairs, 2 lone pairs

T-shaped, 90° and 120°

2 bonded pairs, 3 lone pairs

Linear, 90° and 120°

6 bonded pairs, 0 lone pairs

Octahedral, 90°

5 bonded pairs, 1 lone pair

Square pyramid, 90°

4 bonded pairs, 2 lone pairs

Square planar, 90°

If a reaction explodes it is…

Exothermic

When does the entropy of the surrounding increase?

Since the reaction is exothermic heat energy is released into the surroundings, so the particles in the surroundings gain heat energy / kinetic energy. As a result, there is greater dispersal of matter and energy in the surroundings, so the entropy of the surroundings increases.

When shielding increases so does…

Repulsion, the further from the nucleus the greater the repulsion

Why would a longer molecule with only TD have a higher boiling point than a smaller molecule with PD (or H-bonding)? Despite having similar molar mass

A longer molecule has more surface area for interaction, meaning stronger TD attractions so more energy is needed to break the attractions between the molecules

Why is ∆vapH° more positive than ∆fusH°?

Because fusion, which is melting, only requires SOME bonds to be broken whereas vaporisation (solid to gas or liquid to gas) requires ALL intermolecular forces to be overcome, so more heat energy is required.

When a solid dissolved in water, does the entropy of the system increase or decrease and why?

The ordered ions in the solid lattice form disordered ions in solution. As a result, there is a greater dispersal of matter and energy in the system / more disorder, so the entropy of the system increases (positive entropy change)

Why would a standard enthalpy change be more exothermic (negative) if a molecule was produced as a liquid rather than a gas?

It would be more exothermic because heat energy would be released as intermolecular forces form between liquid molecules.