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Chem106 Assessment 3
| Term | Definition |
|---|---|
| enthalpy (H) | total energy of a system |
| exothermic | delta H is negative products are more stable than reactants, releases heat |
| endothermic | delta H is positive products are less stable than reactants, requires energy |
| entropy (S) | measure of possible microstate arrangement |
| 3 modes of molecular motion (they all happen at the same time) | translational rotational vibrational |
| entropy trends | solid - very ordered, low entropy gas - unordered, low entropy |
| going from a liquid to a gas | increases entropy |
| for elements standard entropy is | 0 J/K |
| entropy increases with | molar mass |
| entropy increases with | number of atoms |
| first law of thermodynamics | energy is conserved, cannot be created nor destroyed |
| second law | the total entropy of the universe increases with any spontaneous process |
| third law | the entropy of a pure crystal substance at 0 K is 0 |
| water and ice above 0 C below 0 C | above 0 C - ice melts spontaneously below 0 C - reverse process is spontaneous (water freezes spontaneously) |
| processes that are spontaneous at one temp may be ____________ at other temps | non-spontaneous |
| when H is + and S is - | G is + non-spontaneous |
| when H is - and S is + | G is - spontaneous |
| when H is + and S is + | G is spontaneous at high temperatures |
| when H is - and S is - | G is spontaneous at low temperatures |
| static equilibrium | object is not moving and all forces acting on it are balanced (ex: book resting on a table) |
| dynamic equilibrium | forces are balanced but the object is moving at a constant speed (ex: sealed soda bottle, gases interacting) |
| chemical equilibrium (type of dynamic equilibrium) | the forward reaction equals the reverse reaction rate concentrations of reactants and products stay constant over time |
| K (equilibrium constant) | C^c D^d / A^a B^b (this is the equilibrium constant expression, solving it gives you the equilibrium constant, k) |
| k is constant for a given | temperature |
| before equilibrium achieved vs after equilibrium achieved | product or reactant shifted product or reactant favored |
| product favored reactant favored | k > 1 k < 1 |
| reactant favored | k < 1 |
| Le Chatlier's Principle | disturbing equilibrium by changing concentration, pressure/volume, or temperature results in an equilibrium shift which counteracts the change |
| changing concentration | does not change k adding a reactant, shifts towards products take a way a reactant, shifts towards reactants |
| half the volume | double the pressure (inversely proportional) |
| pressure and volume changes do not change | k |
| if you increase the pressure | you decrease the volume shift towards fewer moles of gas |
| if you decrease the pressure | you increase the volume shift towards larger amount of moles of gas |
| if both moles on either side of the reaction are even and you change pressure/volume | no shift, remains the same |
| temperature does change | k (think of heat as a reactant/product) |
| in an exothermic reaction the heat is on the | right side (product side) |
| exothermic reactions: increase heat - shifts decrease heat - shifts | increase heat - shifts left decrease heat - shifts right |
| endothermic reaction the heat is on the | left side (reactant side) |
| endothermic reactions increase heat - shifts decrease heat - shifts | increase heat - shifts right decrease heat - shifts left |
| exothermic when temp decreases K _____ when temp increases K ______ | when temp decreases K increases when temp increases K decreases |
| endothermic when temp decreases K _____ when temp increases K ______ | when temp decreases K decreases when temp increases K increases |
| catalysts ________ change the value of k but equilibrium will be achieved _________ | catalysts DO NOT change the value of k but equilibrium will be achieved QUICKER |
| what is the driving force of equilibrium? | Gibb's free energy |
| when a system is at equilibrium, G = and K = | G = 0 K = Q |
| slope = | - deltaH/R so if slope is negative, H is positive |
| at equilibrium macroscopic properties (color, concentration, pressure, pH) remain ______ over time | constant |
| in a heterogeneous equilibrium reaction, which phases will appear in the equilibrium expression? | only gases and aqueous species |
| if you multiply all the coefficients by 2, what do you do to k? | square it |
| what is the difference between K and k? | K - equilibrium constant ratio of products over reactants k - rate constant tells you how fast a reaction happens |
Created by:
anyasalmon