Unit 5- Thermochem Flashcards
Thermochem
the study of the relationship between heat and chemical reactions
kinetic energy
energy possessed by matter bc it is in motion
thermal energy
energy in the form of random motion of particles in any sample of matter
- as temp rises, thermal energy inc
heat
energy that causes a change in the thermal energy if a sample. Adding heat to a sample increases its temp
potential energy
the energy derived from the position or condition of matter
chem energy
a form of potential energy derived from the forces that hold the atoms together in a compound
system
a sample of matter on which we focus our attention, generally the atoms involved in a CHEMICAL REACTION
surroundings
all other matter in universe
law of conservation of energy
the energy of the universe is constant during a chem or physical change
(energy may move between the system and surrounding but total energy not changed)
exothermic reaction
when the system (atoms involved in rxn) transfers heat to surroundings
- key words: produce, provide, give off, release
- loses energy, Enthalpy neg
endothermic reaction
rxn that absorbs heat from surroundings
- key words: need, absorb, require
- gains energy, Enthalpy pos
enthalpy
measure of the energy of the SYSTEM
change in enthalpy (delta H)
equal to the heat absorbed or given off by the system at constant pressure
Thermochem equation
an equation for which enthalpy is given
- enthalpy changes assume that the coeff are MOLEs of the substance (enthalpy/ coeff mole or vice versa)
calorimetry
the experimental measurements of heat released or absorbed by a chem rxn
calorimeter
the device used to measure heat
specific heat (Cs)
the heat needed to inc the temp of 1g of matter by 1k
- units: J/gC or J/gK
heat(q)=mass(m) x Cs x (Tf-Ti)
qsurr
deltaH = qsys = -qsurr
state fxn
a property of the system that is fixed by the present conditions and is indep of the system’s history
(*enthalpy)
path fxn
a property that depends on how the particular change took place
Hess’s Law
when 2 or more thermochem eq are added, the enthalpy change of the resulting eq is the sum of those for the added eqs
standard state
the pure form of a substance at a specified temp at 1atm pressure
- temp usually 25 deg
standard enthalpy of formation
the enthalpy change when 1 molec of a substance in its standard state is formed from the most stable form of its constituent ele in standard states
(deltaH of formation rxn)
-units: KJ/mol
standard enthalpy of formation of ELE
0
standard enthalpy change of rxn
deltaHf^o = sum n x deltaHf^o [PRODUCTS] - sum n x deltaHf^o [REACTANTS]
n=coeff in eq
