Chapter 5 Flashcards
Thermodynamics
study of energy and energy trasnfer
Thermochemistry
study of energy changes that accompany transformations of matter ex. dissolution of NaOH (s) releases heat
Studying energy changes
First law of thermodynamics/law of conservation of energy
- total energy of universe is constant
- energy cannot be created nor destroyed
Can energy be transformed or converted onto other forms
Yes
ex. kinetic E of running water or heat energy
system
the portion of the universe being studied
surroundings
Everything else ex. the lab
universe
= system + surroundings
Heat (Q)
refers to transfer of kinetic energy, unit is J, temp in K= 0C = 273.15K
enthalpy
total internal energy of a substance at a constant pressure, (delta H)
what is an enthalpy change in a chemical reaction
- breaking a bond
- creating a bond
endothermic reaction
results in net absorption of energy-bond breaking in reactants absorb more energy than released in the bond formation of products
exothermic reaction
results in loss of energy-bond formation of products release more energy than absorbed by bond breaking in reactants
which is energy released which is energy absorbed
endo- absorbed (+KJ)
exo- released (-KJ)
delta H reaction
enthalpy of a reaction
delta H
standard enthalpy of reaction
what is a calorimeter
used to measure enthalpy changes for reactions
Q=MC^T
- heat released by a reaction
m= mass (g) of water in caliomter
c= specific heat capacity (J/gc)
^T= change in temp (C= t2-t1)
what assumptions are used with a calorimeter
- no heat is transferred between the calorimeter and the outside environment
- any heat absorbed/released by a styrofoam cup is negligible
- dilute aqueous solutions is assumed to have a density and specific heat capacity of d= 1g/ml and c= 4.184 j/gc
molar enthalpy equation
H= Q/h
- molar enthalpy of reaction (KJ/mol)
what is bond energy
how much energy you have to use to pull apart atoms and break a bond
bond energy equation
sum of bonds broken - sum of bonds formed
specific heat capacity
indicates amount of energy needed to raise the temperature of one gram of substance by 1 degree C
standard enthalpies of formation
quantity of energy absorbed or released when one mole of a compound is directly formed from its elements in their standard states
delta HF
standard enthalpy of formation
from enthalpy of formation equation
delta H reaction f= sum products - sum reactants
