5.2 entropy Flashcards by Iris Cunningham

Define lattice enthalpy

The enthalpy change that occurs when one mole of an ionic lattice is formed from one mole of its gaseous ions (standard conditions)

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Define enthalpy change of formation

The enthalpy change that occurs when one mole of compound is formed from its substituent elements.

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Define first ionisation energy

The enthalpy required to remove one mole of gaseous electrons from one mole of gaseous atoms.

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Define the standard enthalpy change of formation

The formation of one mole of compound from its constituent elements in their standard state

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Define the standard enthalpy change of atomisation

When one mole of gaseous atoms is formed from its constituent elements in its standard state

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Define the second ionisation energy

The enthalpy required to form one mole of gaseous 2+ ions from one mole of gaseous 1+ ions.

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Define first electron affinity

One mol of gaseous 1- ions is formed from one mole of gaseous atoms

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Define second electron affinity

The formation of one mole of gaseous 2- ions from one mole of gaseous 1- ions

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Define standard enthalpy change of solution

the enthalpy change that occurs when one mole of solute is completely dissolved in water (standard conditions)

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Define the standard enthalpy change of hydration

The enthalpy change that occurs when one mole of gaseous ions is dissovled in water (standard conditions)

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What is the enthalpy change of ionic lattice breakdown equal to?

negative lattice enthalpy

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What two aspects dictate the magnitude of lattice enthalpy?

-The size of the ions involved
-The charge density of the ions

(stronger and smaller- easier to form lattice- more exothermic)

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What two aspects dictate the magnitude of enthalpy of hydration?

-The size of the ions involved
-The charge density of the ions

(stronger and smaller= harder to hydrate- less exothermic)

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If a bond requires a large amount of energy to break its less __ and more ___

less exothermic
more endothermic

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How do you work out lattice enthalpy from enthalpy changes of solution and hydration?

∆hydH𝜃 = ∆LEH𝜃 + ∆solH𝜃

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Define entropy

The measure of disorder within a system

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Define standard entropy

Entropy content of one mol of the substance under standard conditions

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Define the standard entropy change of a reaction

entropy change that accompanies a reaction in the molar quantities expressed in a chemical equation (standard conditions)

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what is entropy if there’s more spreading out of energy

higher

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what is entropy if there’s more random arrangements of particles

higher

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how is entropy affected by pressure?

Increases

particles with a higher temperature have higher kinetic energy and move more
the arrangement of particles at a higher temperature becomes more random

entropy of solids, entropy of liquids< entropy of gases

entropy change when dissolving ionic substances?…

Increases

If ionic lattice dissolves, ions can spread out more and the positions of the ions are far more disordered than within the lattice

how does number of gas molecules affect entropy?

more -> increase entropy

Define free energy change

∆G, is the balance between enthalpy, entropy and temperature

Give Gibbs free energy equation

∆G = ∆H - T∆S

how do you calculate entropy?

∆Ssystem + ∆Ssurroundings

For a reaction to occur does entropy have to be greater than or less than 0?

less than

Predicting feasibility: ∆H is -ive, ∆S is +ive

reaction is feasible because in this situation ∆G is always -ive

Predicting feasibility: ∆H is +ive, ∆S is -ive

never feasible as ∆G is always +ive

predicting feasibility: ∆H is -ive, ∆S is -ive

Only feasible at low temps

predicting feasibility: ∆H is +ive, ∆S is +ive

Only feasible at high temps

Other than a -ive∆G, what else may determine the feasibility of a reaction

-may have a high Ea so may require an initial supply of energy (e.g igniting a fuel) -rate may be very slow

What is the colour change in the titration of MnO4- and Fe2+?

Purple (MnO4-) to colourless (Mn2+)

Is MnO4- an oxidising agent or a reducing agent?

Oxidising agent

What does thiosulfate change into when titrated with iodine?

2S2O3- + I2 -> S4O6 2- + 2I-

What are aqueous thiosulfate ions and iodide ions useful for? Describe the process

They can be used to determine the concentration of an unknown reducible species. Initial reaction with unknown oxidising agent and Iodine. Eg: oxidising agent add KI liberates I- ions. Then, thiosulfate (S2O3-) is added along with starch. Starch is blue/black in presence of iodine and so when blue black dissapears, all of the excess iodine has been reacted.

What is the reaction between iodide and Cu2+ ions? What are the colours produced? What can you then do to work out the amount of Cu in the o.g sample?

2Cu2+ 4I- -> 2CuI + I2 produces a light brown/yellow solution and a light brown ppt. of Copper (I) iodide You can then titrate the sample with thiosulfate ions and starch to work out how much Iodine was produced to work out how much Cu there was.

If you want to work out the Cu content of a coin what do you need to do before reacting it with iodine?

you need to obtain Cu2+ ions which can be done by dissolving the coin in nitric acid

Define the standard electrode potential of a half cell

Is the e.m.f of a half cell compared to a standard hydrogen electrode measured in standard conditions

Is it the more positive or negative half cell that reverses direction?

The more negative half cell goes in the oxidation (reverse direction) *all half equations are usually written in the reduction way

What is a salt bridge made of?

filter paper soaked in (usually) KNO3

What happens if you increase Cu2+ concentration the half cell: Cu2+ + 2e- ->Cu

-equilibrium shifts to the right -electrons removed from equilibrium -standard electrode potential is wrong as it becomes more positive

Feasibility of half cell reactions...

slow rate/ high activation energy means standard conditions may not be used in order to increase rate,

What does E𝜃 have to (usually) be in order for a reaction to occur?

more than 0.4

More negative E𝜃 is, the more likely the half cell is to undergo...

oxidation

How do non-rechargeable fuel cells work?

Provides chemical energy until all the chemicals have reacted and the voltage falls.

How do rechargeable batteries work?

Chemicals in cell react, providing electrical energy. Cell reaction can be reversed during recharging Chemicals are regenerated so can be used again.

Risks and benefits of using electrochemical cells

+ive: -provide energy -ive: -toxicity upon ingestion of Li -rapid discharge of current leading to possible explosions and fires

How do fuel cells work?

fuel + oxygen -> voltage fuel in, product out, electrolyte remains in the cell. can occur continuously as long as fuel and oxygen continue to flow into the cell.

What are the two half equations in a fuel cell? Combine them.

1/2O2+ H2O(l) +2e- -> 2OH-(aq) +ive 2H2O(l) + 2e- -> H2(g) + 2OH-(aq) -ive (also -ive electrode/ anode) overall: H2 + 1/2O2 -> H2O

define the enthalpy change of hydration

1 mole of gaseous ions forming 1 mole of hydrated ions