Chemistry Thermochemistry Flashcards
A ___ is the particular part of the universe being studied; everything outside the system is considered the surroundings or environment. A system may be:
Isolated: it cannot exchange energy or matter with the surroundings, as with an insulated bomb reactor
Closed: It can exchange energy but not matter with the surroundings, as with a steam radiator
Open: It can exchange both matter and energy with the surroundings, as with a pot of boiling water
thermodynamic system
Properties whose ___ depends only on the initial and final states of the system and not on the path of the change are known as state functions
magnitude
___ = delta E sub sys + delta E sub surr = 0
delta E sub univ
delta E sys = q (__) + W (work)
heat
Reactions that absorb heat energy are said to be ___, while those that release heat energy are said to be exothermic
endothermic
q=mcdelta T
The ___ absorbed or released in a given process is calculated from this equation
where m is the mass, c is the specific heat capacity, and delta T is the change in temperature. Specific heat is a property of a material that describes how much energy it takes to raise its temperature
heat
___ lost by a system (to its surroundings) or work done by the system (on the surroundings) is considered negative (decreases internal energy
heat
delta H rxn = H sub products - H sub reactants
A positive delta H corresponds to an ___ in which enthalpy is added to the system and a negative delta H corresponds to an exothermic process in which the system gives off enthalpy
endothermic process
___ occur in systems at constant pressure (delta P = 0). Heat given off or absorbed equals the change in enthalpy of the system.
Isochoric processes occur at constant volume (delta V = 0). Heat given off or absorbed equals the change in internal energy of the system and also equals the change in enthalpy of the system.
Isothermal processes occur when system do not change temperature (delta T = 0). The change in internal energy, as well as enthalpy, equals zero (only for an ideal gas) but head does not equal 0.
Adiabatic processes occur when there is no heat exchanged between systems and their surroundings (delta q = 0). The change in internal energy is equal to work
isobaric processes
The ___ of a compound, delta H degree sub f, is the enthalpy change that occurs if one mole of a compound is formed directly from its elements in their standard states
enthalpy of formation
Note that the enthalpy of ___ of n element in its standard state is defined as zero, so the heat of formation of a compound gives its increase or decrease in enthalpy from zero
formation
Note that the ___ must be balanced for one mole of the product because the enthalpy of formation is defined for one mole of a substance
equation
delta H degree sub rxn = (sum of delta H degree sub f of products) - (sum of delta H degree sub f of reactants)
One specific type of ___ of reaction is the standard heat of combustion, delta H degree sub comb
enthalpy
___ states that enthalpies of reactions are additive; if a reaction is broken down into individual steps, the overall enthalpy of the reaction is the sum of enthalpies for each step
Hess’s Law
___ is the energy required to break a specific chemical bond in one mole of gaseous molecules
bond dissociation energy
Since it takes energy to pull two atoms apart, ___ breaking is always endothermic and bond formation is always exothermic
bon
delta H sub rxn = (delta H of bonds broken) - (delta H of ___ formed) = total energy input - total energy released
bonds
___ (S) is a measure of the disorder, or randomness, of a system
entropy
For any substance, ___ (solid to gas) will be the phase transition with the greatest entropy change
sublimation
A system reaches its maximum entropy at ___, a state in which no observable change takes place as time goes on
delta S sub universe = delta S sub system + delta S sub surroundings = 0
equilibrium
A system will spontaneously tend toward an equilibrium ___ if left alone
state
delta S degree sub rxn = (sum of S degree sub products) - (sum of S degree sub ___)
reactants
The thermodynamic state function G, known as Gibbs free energy, provides information on how both enthalpy and entropy ___ affect a reaction
changes
delta G = delta H - TdeltaS
where T is the absolute ___in kelvin
temperature
In the equilibrium state, free ___ is at a minimum
energy
- If delta G is negative, the ___ is spontaneous and proceeds forward
- If delta G is positive, the reaction is not spontaneous, and the reverse reaction occurs
- If delta G is zero, the system is in a state of equilibrium; thus delta G = 0 and deltaH = TdeltaS
reaction
The rate of a ___ depends on the activation energy, not on deltaG. Spontaneity indicates whether or not a reaction will occur but not the rate of the reaction
reaction
Spontaneity indicates whether or not a reaction will occur but not the ___ of the reaction
rate
Enthalpy and ___ may act together to drive a reaction forward or backward, or they may oppose each other
entropy
The temperature will determine whether entropy or ___ has a greater effect on the spontaneity of a reaction, and the reaction is considered to be temperature-dependent
enthalpy
