Chem 30 Unit 1 Flashcards
the original source of energy on earth is….
the sun
chemical energy
energy released when substances undergo a chemical reaction (e.g. combusion) to transform into other substances (e.g. burning of fossil fuels)
Nuclear energy
form of energy released from the nucleus of atoms.
nuclear fission
the splitting of an atomic nucleus into two smaller nuclei (releasing nuclear energy)
nuclear fusion
combining two atomic nuclei to produce one larger nucleus (releasing nuclear energy)
solar energy
energy from teh sun
geothermal energy
heat energy from the earth (e.g. geysers, hotsprings)
Laws of Thermodynamics
- Law of Conversation of Energy
- Law of Heat Exchange or Transfer
- Total heat lost = total heat gained
Law of Conversation of Energy
Energy cannot be created or destroyed; can be converted
from one form to another.
Law of Heat Exchange or Transfer
Heat flows from hot to cold until thermal equilibrium
Total heat lost = total heat gained
energy lost by the hot object is equal to the energy gained by the cold object.
Exothermic
energy produced, given off by the reactants. Releases heat to the surroundings. Has a negative ΔH.
Endothermic
energy is required, reaction needs energy to occur. Absorbs energy from the surroundings. Has a positive ΔH.
cellular respiration is…
exothermic
photosynthesis is…
endothermic
Kinetic molecular theory
the smallest particles of any substance are in continuous motion
translational motion
straight line motion (gases)
rotational motion
spinning or turning (liquids)
vibrational motion
oscillation (back/forth) motion (solids)
temperature is …
the average kinetic energy of the particles of the substance.
Change in temperature =
change in average kinetic energy
specific heat capacity
the quantity of heat required to raise/lower the temp of a substance per unit mass per degree celsius.
calorimetry
a substance is burned in pure oxygen in a reaction chamber. heat released flows into surrounding water, changing its temperature. use data collected to calculate heat given off.
Enthalpy (ΔH):
measure of the energy content of a system
open system
allows both energy and matter to flow in and out of the system
closed system
only allows the transfer of energy in and out (does not allow transfer of matter)
enthalpy of a system is
the total kinetic energy and potential energy of a system under constant pressure
kinetic energy
energy of an object due to motion (change in temp)
potential energy
energy of an object due to position (chemical change)
molar enthalpy
= molar heat of combustion
molar enthalpy/molar heat is…
positive/negative depending on if water was heated/cooled
positive enthalpy change means….
endothermic reaction
negative enthalpy change means….
exothermic reaction
for calorimetry questions that include both the water and calorimeter…
chemical energy = calorimeter (water + calorimeter)
molar enthalpies for decomposition
switch sign of data book value
potential energy diagrams…
shows the change in potential energy during a chemical reaction.
in an exothermic potential energy diagram…
there is a step down (reactants have more Ep than products)
in an endothermic potential energy diagram…
there is a step up (reactants have less Ep than products)
Axis for a potential energy diagram:
x axis: progress of reaction
y axis: potential energy (Ep)
difference between the Ep of reactants and products =
ΔH (change in enthalpy)
catalyst
makes the reaction happen faster, but does not hange the reaction. Does not
change the ΔH.
Activation energy
energy needed to get the reaction started (do not include when calculating ΔH in a Ep diagram).
Hess’s Law
the enthalpy of reaction is the same regardless of whether a reaction occurs in one step or in several steps.
ΔH =
products - reactants
ΔH of elements =
0 kJ
