scientific perspective
research, explaining natural phenomena
technological perspective
development and use of machines, instruments and processes that have a social purpose
ecological perspective
relationship between living organisms and the environment
economic perspective
production distribution and consumption of goods/wealth
political perspective
involves vote and getting actions/measures
STEEP
scientific, technological, economical, ecological, political perspectives
ways to approach societal issues in science and technology
energy
the ability to do work
can be transformed from one form to another
direction of flow determines wether it is exothermic or endothermic
first law of thermodynamics
during and energy transfer, the total energy of a system remains constant
2nd law of thermodynamics
enery will flow from hot to cold until thermal equilibrium is reached (substance and environment - usually water - are the same temp)
endothermic
energy is absorbed
feels cool
separates bonded particles (↑ potential energy)
ex. ice pack
exothermic
energy is given off
feels warm
bonds particles together ( ↓ potential energy)
ex. hot pack
sources of energy
chemical - fossil fuel, food
nuclear - uranium, plutonium, hydrogen
solar - radiant energy, UV radiation
geothermal - hot springs, geysers, volcanoes
what is the origin of chemical energy
the sun (radiant energy)
how the sun transfers energy throughout the biosphere?
sun → photosynthesis → cellular respiration → biological decay → formation of fossil fuels → combustion → release of stored energy
photosynthesis
carbon dioxide and water react in plant in the presence of sunlight to produce glucose and oxygen
endothermic reaction
cellular respiration
glucose is stores are accessed from photosynthesis
glucose and oxygen react to form carbon dioxide, liquid water and energy
exothermic reaction
hydrocarbon combustion
the burning of fossil fuels
water vapor is formed in this type of reaction
chemical change
reactants have different chemical compositions than the products
rearrangement of molecules
involves a change in temperature (exo or endothermic)
total potential energy of reactants is different than the products due to different chemical compositions
ex. combustion, neutralization, decomposition, formation
endothermic reactionary pathway
heat is absorbed during this type of reaction
change in enthalpy is positive because energy is gained
exothermic reactionary pathway
heat is released during this type of reaction
change in enthalpy is given off because energy is lost
kinetic energy
energy of motion/motion due to heat
when molecules change in temperature the tend to speed up/slow down
potential energy
energy stored in a position or state
when a chemical change in phase or change in chemical composition (chemical rxn occurs) there is a change in this type of energy
chemical changes release more energy that phase changes
intermolecular bonds
bonds between molecules
relatively weak bonds (release less energy)
intramolecular bonds
bonds between elements within molecules
relatively strong bonds (release more energy)
calorimetry
the process used to measure the changes in enthalpy (heat energy)
measured in joules (J) or kilojoules (KJ)
specific heat capacity
the amount of energy (J) required to change 1.00g of a substance by 1.00 degrees celsius
thermal energy (Q)
the total kinetic energy of a substance
measured by Q = mct
what is the density of water
1ml = 1g
1L = 1kg
thermochemistry
the study of energy changes by a chemical reaction during a chemical reaction
energy changes occur by energy being absorbed from or released to the surroundings
enthalpy
heat energy of a system
calorimeter
an instrument used to measure the amount of energy lost or absorbed during a phase change or chemical reaction
by knowing how much energy water gains or loses, we can determine the energy lost or absorbed by the substance
simple calorimeter
used primarily for phase changes
basic requirements include:
measured amount of liquid (water)
thermometer
isolated system
metal can calorimeter
usually for reaction that involve temperatures > 100 degrees celsius
you cannot assume this type of calorimeter is an isolated system because heat energy is transferred to both the water and the container
bomb calorimeter
usually for volatile combustion reactions
it is more precise and contains fixed components
what does an increase in a calorimeters water temperature indicate?
release of energy by the system
increase of heat
exothermic reaction
what does a decrease in a calorimeters water temperature indicate?
absorption of energy by the system
decrease of heat
endothermic reaction
calorimetry assumptions
system is isolated - all energy lost or gained by the chemical system is gained by the calorimeter
conservation of mass - all material (ie. mass) of the system is conserved
specific heat capacity of water over a temperature range remains @ 4.19J/g degrees celsius
specific heat capacity of dilute solutions is 4.19 J/g degrees celsius
density of solute is the same as water
thermal energy lost/gained by the rest of the calorimeter is negligible
efficiency
the ratio of useful energy produced (energy output) to energy used in its production (energy input) in % form
efficiency = energy out/energy in x 100%
what does a positive enthalpy indicate?
endothermic reaction
energy is gained by the chemical system
what does a negative enthalpy indicate?
exothermic reaction
energy is lost by a chemical system
molar enthalpy
the enthalpy change per one mole of a substance
H = Hm x n
neutralization calorimetry
the surroundings of the calorimeter becomes the combination of the volumes of the two solutions
solutions are dilute meaning they have the same density as water
metal can calorimetry
some problems involve containers which absorb energy as well as the solution that the substance is placed in
in these types of calorimeters, you need to calculate the energy absorbed by the container in addition to the solution