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Description
Flashcards by Kellie Mayes-Barwick, updated more than 1 year ago
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Created by Kellie Mayes-Barwick
over 7 years ago
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| Question | Answer |
| What is the definition for Lattice Enthalpy, (∆leH°)? | is the enthalpy change that accompanies the formation of one mole of an ionic lattice from its gaseous ions under standard conditions |
| What is the definition of Standard Enthalpy of Formation, (∆fH°)? | is the enthalpy change that accompanies the formation of 1 mole of a compound from its constituent elements in their standard states -usually exothermic for an ionic compound because bonds are formed |
| What is the definition for First Ionisation Energy, (∆I1H°)? | is the energy change that accompanies the removal of one mole of electrons from one mole of gaseous atoms -endothermic process because the e- being lost has to overcome the attraction from the nucleus in order to leave the atom |
| What is the definition for the first electron affinity, (∆EA1H°)? | is the opposite of ionisation energy, the addition of e- rather than the removal of e- is the energy change associated with the addition of one more of electrons, to form one mole of gasepus atoms from one mole pf gaseous 1- ions |
| What is the definition for the Standard Enthalpy Change of Solution, (∆solH°)? | is the enthalpy chamge that takes place when one mole of a solute is completrly dissolved in water under standard conditions two processess take place when a solid dissolves: 1. Ionic lattice breaks down 2. Free ions become part of solution (hydration) -lattice enthalpy has a negative sign and is exothermic |
| What is the definition for the Standard Enthalpy Change of Hydration, (∆hydH°)? | is the enthalpy change that takes place when dissolving one mole of gaseous ions in water break down of the ionoc lattice has a positive sign and is endothermic Ionic lattices dissolve in polar solvents such as, water Energy is released when new bonds form between water and the ions |
| What dictates the size of the lattice enthalpy? | magnitude of lattice enthalpy depends on: 1. Size of ions involved 2. Charges on the ions 3. Ionic bond strength (dependent of ionic size and charge) -Smaller ions (can get closer together, have smaller ionic radius) attracts one another more strongly, gives rise to more exothermic lattice enthalpy values -Ions with higer charges have stronger electrostatic attractions and so more exothermic lattice enthalpy values most exothermic values are from, small ions with a high charge applies to enthalpy of hydration (so ions with water molecules) |
| What is the definition of entropy, S? | is the quantitive measure of the degree of disorder in a system the more disorded the particles are in a system, the higher the entropy of the system solid has a low disorder compared to gas |
| What is the definition of Standard Entropy, S°? | of a substance is the entropy content of one mole of the substance under standard conditions have the units, J K-1 mol-1 all substances above 0K possess a certain degree of disorder because they are in constant motion, so: 1. entropy, S, is always a positive number 2. at 0K, entropy is 0 for perfect crystals more probable a more disorded system will be found instead of a more ordered system more spreading out of energy= higher entropy more random arrangements of particles= higher entropy |
| What is the Standard Entropy Change of Reaction, ∆S°? | is the entropy change that accompanies a reaction in the molar quantities expressed in a chemical equation under standard conditions, all reactants and products being in their standard states entropy can change during the course of a chemical reaction, noted as a change in entropy although there is a tendency towards higher entropy, it is possible for entropy to decrease, for ∆S to be negative. E.g: Water to Ice, disordered liquid becomes a more ordered solid, has lower levels of energy dispersal ∆S = sum of S°products- sum of ∆S reactants change makes a system more random = ∆S is + change makes a system more ordered = ∆S is - |
| How is entropy affected by temperature? | Entropy of pure substances increase with increasing temperature values are given per K-1 (because entropy values are dependent on temp) -arrangement of particles at higher temp becomes more random -Entropy of solids < liquids < gases |
| How do the number of gaseous molecules affect the entropy? | numbrr of gaseous molecules changes during a reaction then entropy increases increase in gaseoua molecules= increase in entropy decrease in gaseous molecules= decrease in entropy |
| What is free energy change, ∆G? | is the balance between, enthalpy, entropy and temperature for a process: ∆G = ∆H - T∆S a process can take place spontaneously when ∆G < ∆ for a process to occur spontaneously entropy must increase, however there are many reactions that happen spontaneously that would seem to lower energy |
| What is the total change in entropy? | ∆S°total= ∆S°system -∆S°surroundings reactions that have a decrease in entropy can happen spontaneously if the change in entropy of the surroundings is positive enough the make the total change is entropy positive |
| How is the Gibb's equation and Free Energy Change associated? | energy that becomes 'free' during a reaction is known as Gibbs' free energy after theoretical physicist and mathematician, John Willard Gibbs dependent on total entropy, enthalpy changes that occur and temperature for reactions to occure spontaneously, ∆G must be negative ∆G = ∆H - T∆S ∆S°total= ∆S - (∆H÷T) rearranged to: -T∆Stotal = ∆H - T∆S converted to Gibbs equation: ∆G = -T∆S |
| How can you use Gibbs equation to predict feasibility of reactions? | -Large increases in entropy will cause decreases in ∆G, because the term -T∆S will become larger -Large negative values for ∆H(highly exothermic reactions), will result in more negative values for ∆G If a highly exothermic reaction causes a large decrease in entropy, ∆G, may be positive, in which case the change would not be spontaneous |
| in summary of last flashcard: | -exothermic reactions are generally spontaneous-negative values of ∆H is still able to make ∆G negative, even if the entropy change is positive -endothermic changes are only positive if the entropy changes are positive and the temperature is high enough to make T∆S large and positive, i.e greater than ∆H |
| What are the limitations of using ∆G to predict feasibility of reactions? | -calculating values ale of ∆G gives a theoretical value for whether a reaction will occur spontaneously -If a reaction is found to have a negative value of ∆G, it does not mean it will go on to react -whether or not a reaction process also depends on kinetic factors: 1. Reaction may have a high Ea 2. Rate of reaction may be very slow Read cross that have a positive value of ∆G are considered not feasible, but can be made to take place by changing the temperaturtemperaturen of the reaction |
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