Chapter 15: Energy and Chemical Change Flashcards
Energy
Ability to do work or transfer heat
Work
Energy used to cause an object that has mass to move (Force x distance)
Heat (Enthalpy In Reactions)
Energy used to cause the temperature of an object to rise (Q = mc[deltaT])
Q = Heat (cal or J)
m = mass (g)
c = specific heat (cal/g[degreesC] or J/g[degreesC])
deltaT = Temperature change
Kinetic Energy
Energy objects (including atoms and molecules) possess by virtue of their motion
Potential Energy
Energy an object possesses by virtue of its position or chemical composition - stored in chemical bonds
Calories To Joules
1 cal = 4.184 J
System
Molecules we want to study
Surroundings
Everything besides what we want to study
Specific Heat/Heat Capacity
A measure of how easily a substance changes temperature
Specific Heat & Conductors Or Insulators
High c = Insulator
Low c = Conductor
Specific Heat Of Water
1.0 cal/g(degreesC) or 4.18 J/g(degreesC)
First Law Of Thermodynamics
Energy cannot be created or destroyed, so total energy of universe is a constant, but energy can be transferred from one system to another
Endothermic
Absorbs heat; +deltaH; Feels cold
Exothermic
Heat released; -deltaH; Feels hot
Energy (Term)
Added, never subtracted; can be used in stoichiometry
Hess’s Law
if a reaction is carried out in a series of steps, ΔH for the overall reaction will be equal to the sum of the enthalpy changes for the individual steps
deltaHf^o
Standard (1.0 atm & 25 degreesC) enthalphy of formation
deltaHrxn
deltaHf^o products - deltaHf^o reactants
Entropy
Amount of disorder in a system; increasing in universe as a whole; decrease entropy in a system by adding energy
Chemical Entropy
Solid < Liquid < Gas
Increase # particles = increase entropy
Increase # substance = increase entropy
Increase temp = increase entropy
Driving Forces For Reaction
- Enthalpy (deltaH)
- Entropy (deltaS)
- Free Energy (delta G)
- Temperature
Spontaneous Reaction
May occur without addition of extra energy
Factors Affecting Entropy
Higher temp, volume, # of particles + disolution results in higher entropy
*Free Energy (Chapter 3-15) (delta G)
deltaG = deltaH - TdeltaS
Positive deltaH, Positive deltaS
-deltaG & spontaneous @ high temp
Negative deltaH, Negative deltaS
-deltaG & spontaneous @ low temp
Positive deltaH, Negative deltaS
Always +deltaG & never spontaneous
Negative deltaH, Positive deltaS
Always -deltaG & always spontaneous
