Unit 5 - thermodynamics

jasmin.sahota
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Flashcards on Unit 5 - thermodynamics, created by jasmin.sahota on 06/14/2013.

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jasmin.sahota
Created by jasmin.sahota over 6 years ago
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Question Answer
standard enthalpy of an element is... zero
H2(g) + 0.5O2(g)--> H20(l) what is this an example of? standard molar enthalpy of formation
the standard enthalpy of atomisation is... the enthalpy change which accompanies the formation of one mole of gaseous atoms from the element in its standard state under standard conditions
Mg(s) -->Mg(g) is an example of... the standard enthalpy of atomisation
definition of first ionisation energy... is the standard enthalpy change when one mole of gaseous atoms is converted into a mole of gaseous ions each with a single positive charge.
Na(g) --> Na+(g) + e- is an example of... first ionisation energy
definition of second ionisation energy refers to the loss of a mole of electrons from a mole of singly positively charged ions
Na+(g) --> Na2+(g) + e- is an example of.. second ionisation energy
O(g) + e- ---> O-(g) is an example of first electron affinity note it refers to single atoms, not oxygen molecules, O2
definition of lattice formation enthalpy is... is the standard enthalpy change when one mole of solid ionic compound is formed from it's gaseous ions
O-(g) + e- --> O2- (g) is an example of the second electron affinity
Na+(g) + Cl-(g) --> NaCl(s) is a definition of lattice formation enthalpy
(Na+) + aq --> Na+ (aq) is an example of enthalpy of hydration
definition on the enthalpy of solution is... is the standard enthalpy change when one mole of solute dissolves completely in sufficient solvent to form a solution in which the molecules or ions are far enough apart not to interact with each other.
NaCl(s) + aq --> Na+(aq) + Cl-(aq) is an example of enthalpy of solution
definition of mean bond enthalpy is the enthalpy change when one mole of gaseous molecules each breaks a covalent bond to form two free radicals, averaged over a range of compounds
standards conditions = 100kPa and 298k
ionic bonding is between metal and non metal ions
the metal ions in ionic compounds are... positively charged ions that have a stable outer shell of electrons
the non-metal ions in an ionic compound are.. negatively charged ions with a stable outer shell of electrons
Hess's law states the total enthalpy change for a chemical reaction is the same whatever route is take
Born - Haber cycle is a thermochemical cycle that includes all the enthalpy changes involved in the formation of an ionic compound
A born-haber cycle starts with the elements in there standard states, so starts from zero
draw the born haber cycle for NaCl born_haber_cycle_for_NaCl.png (image/png)
draw the born haber cycle for MgCl when we know 1. delta Hf = -641kJmol-1 2. delta H at (Mg) = +148 kJmol-1 3. first IE (Mg) = +738Kjmol-1 4. second IE (Mg) = +1451 Kjmol-1 5. atomisation of Cl = +122Kjmol-1 6. first EA of Cl = -349kJmol-1 7. lattice formation = -2524kJmol-1 born_haber_cycle_for_NaCl.png (image/png)
all first electron affinities of all element are negative because... the added electron is attracted by the nuclear charge.
looking at the trends in lattice energy, a larger ion means... a smaller lattice enthalpy
why does a larger ion lead to a smaller lattice enthalpy... because the opposite charges do not approach each other as closely when the ions are larger.
the lattice enthalpy increases with the size of the charge, why? because ions with double the charge give out roughly twice as much energy when they come together
negative delta H is a clue as to whether a reaction is spontaneous or not
gases are more ..... than liquids random because of the arrangement of their particles
the randomness of a system is called entropy
is the particles of the products is more disordered than the reactants then the entropy change is... positive
what has a larger entropy, liquids, gases, or solids? gases>liquids>solids
units of entropy are JK-1mol-1 or kJK-1mol-1
the entropy change for a reaction can be calculated by adding all the entropies of the products and subtracting the sum of the entropies of the reactants.
what are the two factors that dictate whether a reaction is feasible? enthalpy change and entropy change
is delta G = negative this means? the reaction is feasible
if delta G = positive this means? the reaction is not feasible
gibbs depends on temperature therefore some reactions may be feasible at one temperature and not at another
when delta G = 0 what does this mean? this is the point at which the reaction is feasible.
enthalpy and entropy tell us nothing about the rate of the reaction.. why? because there may be a high activation energy barrier
delta S is the sum of the entropies of the products - the sum of the entropies of the reactants