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Terms in this set (28)
process describes a process or reaction in which the system absorbs energy from its surroundings; usually, but not always, in the form of heat. Photosynthesis, the reaction which allows plants to use sunlight to produce food and energy. The energy that is taken in is light energy from the sun.
Ex. baking bread, evaporation of water, melting ice cube
a chemical reaction that releases energy by light or heat. It is the opposite of an endothermic reaction. Expressed in a chemical equation: reactants → products + energy.
Ex. a candle flame, rusting, making ice cubes
an amount of heat equal to 4.184 joules
means 1000 calories (with a lowercase "c"), also known as a "kilocalorie" (also with a lowercase "c"). use this when referring to food
standard unit of energy
conversion between calorie, Calorie, and joule
1 calorie = 4.184 J
1 Calorie = 4184 J
1000 calories = 1 Calorie or kilocalorie
q, m, s, deltaT conversions
q=joules or kilojoules
s or c= 4.184 J/gC
(symbol: Q) is energy. It is the total amount of energy (both kinetic and potential) possessed by the molecules in a piece of matter. Heat is measured in Joules. Heat is energy that is transferred from one body to another as the result of a difference in temperature.
(symbol: T) is not energy. It relates to the average (kinetic) energy of microscopic motions of a single particle in the system per degree of freedom. It is measured in Kelvin (K), Celsius (C) or Fahrenheit (F).
Temperature is a measure of hotness or coldness expressed in terms of any of several arbitrary scales like Celsius and Fahrenheit.
changes in internal heat, energy, and work
deltaE = q + w
q negative- heat lost
q positive- heat gained
w negative- work done by system
w positive- work done on system
deltaH reaction (+, -, 0)
deltaH = Hprod - Hreac
deltaH positive- endothermic, absorbs heat from surroundings
deltaH negative- exothermic, releases heat to surroundings
deltaH 0= temperature will not have an effect on the equilibrium position
0 degrees celsius or 273.15 K
1 atm pressure
15 degrees C (288.15 K, 59 F)
101.325 kPa (1 atm, 760 torr)
a state function is a property whose value does not depend on the path taken to reach that specific function or value.
calculate deltaH rxn using heating/cooling curves
calculate deltaH rxn using calorimetry
qsys = -qsurroundings
calculate deltaH rxn using deltaH f
balance out top equation reversing or multiply them to get them to cancel out and add enthalpies
calculate deltaH rxn by combining known deltaH rxn values
delta H prod - delta H rxn
calculate deltaH rxn by using bond energies
bond energies of reactants - bond energies of products
spontaneity and spontaneous processes
A spontaneous process is the time-evolution of a system in which it releases free energy (usually as heat) and moves to a lower, more thermodynamically stable energy state. The sign convention of changes in free energy follows the general convention for thermodynamic measurements, in which a release of free energy from the system corresponds to a negative change in free energy, but a positive change for the surroundings.
Just needs one input of energy
explain why entropy changes with temperature, phase change, etc.
The higher the temperature the more thermal energy the system has; the higher the entropy. Increasing the temperature will increase the entropy.
The larger the volume the more ways there are to distribute the molecules in that volume. An increase in volume will increase the entropy. This is typically only important for systems involving gases since they are the only materials that undergo large volume changes. Some phases have larger numbers of microstates and thus higher energy. Solids have the fewest microstates and thus the lowest entropy. Liquids have more microstates (since the molecules can translate) and thus have a higher entropy. When a substance is a gas it has many more microstates and thus have the highest entropy.
predict deltaS in processes (+, -, 0)
In general, ΔS is positive if:
(1) more gas moles are produced than reacted.
(2) a solid turns into a liquid or gas
(3) a liquid turns into a gas
(4) a solid dissolves
(5) there are more product moles than reactant moles
(6) the temperature of a substance is increased
calculate deltaS using S-not values
s prod - s reac
explain relationship between enthalpy and entropy
(Gibbs) Enthalpy is a measure of heat content of the system, whereas entropy is the measure of change in (enthalpy/temperature). The energy associated with a chemical reaction that can be used to do work. The free energy of a system is the sum of its enthalpy (H) plus the product of the temperature (Kelvin) and the entropy (S) of the system:
G = H - TS
predict deltaG in processes
deltaG = deltaH - TdeltaS
deltaG = sum G prod - sum G reac
find the temperature range at which a reaction is spontaneous
The reaction becomes spontaneous when ΔG is negative. First find ΔS and then use that to find what temperature the reaction will become spontaneous by finding the temperature that ΔG will become negative.
calculate deltaG using deltaG final of products and reactants and using Gibbs equation. relate this to spontaneity.
delta G and spontaneity
deltaG- positive non spontaneous
deltaG- negative spontaneous
deltaG- 0 at equilibrium
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