ch 5 thermochemistry Flashcards
thermodynamics
study of energy and its transformations. Thermochemistry: relationships between chemical reactions and energy changes
energy definition
capacity to do work or to transfer heat
kinetic energy3
energy of motion. Ek=1/2mv2. m=mass, v=velocity. Kinetic energy increases as speed increases. Atoms/molecules have mass and are in motion=have kinetic energy
potential energy2
energy by virtue of position relative to other objects. Arises when there is a force (push or pull) acting on an object. Ep=mgh. m=mass, g=gravitational constant=9.8m/s2. h=height
electrostatic potential energy4
arises from interaction between charged particles. Eel is proportional to the electrical charges on the two interacting objects and inversely proportional to the distance between themEel=(kQ1Q2)/d. k=constant of proportionality, =8.99*109J–m/C2. (C =coulomb, unit of electrical charge. J=joule). When Q1 and Q2 have the same sign, they repel one another, and Eel is positive. When they have opposite signs, they attract and Eel is negative.Lower energy of system=more stable.
SI unit for energy3
Joule, J. 1J=1kg–m2/s2. Energy associated with chemical reactions is kilojoules.
non SI unit for energy4
calorie (cal)=amount of energy to raise temperature of 1g of water from 14.5ºC to 15.5ºC. 1 cal=4.184J. 1Cal=1000cal=1 kcal
closed system
can exchange energy but not matter with its surroundings, does not lose or gain mass
work2
energy used to cause an object with mass to move. w=F*d
heat
energy used to cause the temperature of an object to increase. Transferred from hot object to cold objects
first law of thermodynamics
energy is conserved. Any energy lost by the system must be gained by the surroundings, and vice versa.
internal energy defs
sum of all kinetic and potential energies of components of system. Represented as E. When E is positive=system gained energy from surroundings. When E is negative=system lost energy to surroundings. Initial state=reactants, final state=products.
internal energy formulas2
E=Eproducts-Ereactants
E=q+w.
endothermic3
system absorbs heat. (melting of ice). Feels cold because heat transferred from our hands (surroundings) to system. E>0
exothermic3
system loses heat. (combustion). Feels hot as temp of system drops and enters surroundings.
E<0
state function
property of a system that is determined by the specifying the system’s condition/state. Value of state function depends only on present state of system, not on path system took to reach that state
pressure-volume work3
work involved in the expansion or compression of gases. When pressure is constant, w=-PV. P=pressure, V=change in volume (Vfinal-Vinitial). When volume expands, V is positive and w is negative, meaning energy leaves system as work and vice versa for when a gas is compressed.
enthalpy5
thermodynamic function that accounts for heat flow in processes occurring at constant pressure when no forms of work are performed other that P-V work. Denoted by symbol H.
H=E+PV.
H=E+PV=(qP+w)-w=qp. qp emphasizes changes at constant pressure.
Change in enthalpy =heat gained/lost at constant pressure
H>0(meaning when qP>0), heat is gained=endothermic
enthalpy of reaction/heat of reaction
Hrxn=Hproducts-Hreactants
thermochemical equations
balanced equations that show the associated enthalpy change where the coefficients represent the number of moles of reactants/products producing the associated enthalpy change.
enthalpy diagram
another way of representing enthalpy change through a diagram. If reaction is exothermic, reactants are written higher than products with an arrow drawing down to indicate loss of heat
facts about enthalpy change5
The enthalpy change of a reaction is equal in magnitude but opposite in sign to H for the reverse reaction.
When H is large and negative, it is spontaneous/thermodynamically favored
When H is large and positive, it is spontaneous in the reverse direction
Gases have greater internal energy than liquids, so if liquids were changed to gas on the reactant side, H would decrease but if liquid changed to gas on product side, H would increase
calorimetry
measurement of heat flow. Calorimeter: device used to measure heat flow
heat capacity2
represented as C, the temperature change experienced by an object when it absorbs a certain amount of heat. Amount of heat required to raise its temperature by 1 K (or 1ºC). Greater heat capacity, the greater the heat required to produce a given increase in temp