Chemistry 30-1: Chapter 11

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