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Enthalpy Changes and their Applications

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livia rrokaj

on 4 November 2012

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Transcript of Enthalpy Changes and their Applications

Enthalpy Changes

Applications and their Definition Enthalpy is the amount of heat content absorbed or released in a system at constant pressure
Enthalpy Change is therefore, the difference in enthalpies of reactants and products during a type of change Delta H systems = ± I q surroundings I Delta H: Enthalpy change
q: Quantity of heat transferred Exothermic reaction: releasing thermal energy as heat flows out the system
Endothermic reaction: absorbing thermal energy as heat flows into the system Physical Change Chemical Change Nuclear Change Physical Change Chemical Change Nuclear Change A change in the form of a substance where chemical bonds are not broken
A new substance is not formed
Examples: melting, freezing, vaporization, condensation, and sublimation A change in the chemical bonds between atoms, creating a new substance
This reaction takes place on the molecular level
Examples: Combustion (burning), oxidation(rusting), neutralization, etc. Evidence
Change in colour
Change in smell or taste
Light production
Gas production A new atom is formed in this reaction because of change in protons and neutrons Evidence
Formation of a new element with different numbers of protons and neutrons Evidence
Change in shape and size (volume)
Change in texture
Change in mass Involves about 1 million times as much energy as a chemical change Nuclei can break apart (nuclear fission) to form smaller elements, or combine (nuclear fusion) of neutrons and protons to form heavier atoms Nuclear Fusion A combination of two smaller atoms into a larger one
ex. stars experience this when hydrogen atoms are converted to helium atoms Nuclear Fission One atom splits creating two or more smaller ones, emitting 100 million or more volts of energy
ex. the atomic bomb experiences the nuclear fission chain reaction
The chain reaction occurs when "spare" neutrons from an atom fly out with sufficient force to split U-235 (uranium) atoms they come in contact with Beta Particles Beta particles are high-energy, high-speed electrons or positrons emitted by certain types of radioactive nuclei most likely Strontium-90 Uses:
"Betalight" which contains tritium and phosphor is an illumination device
Tritium emits beta particles when it decays which strike phosphor, causing it to give off photons and an illumination
Beta particles are used in manufacturing
ex. controls how thickness of paper
They are also used to treat health conditions such as in eye and bone cancer Tempering: steel is repeatedly hit and hammered to make it more durable, reduce its flexibility and ability to maintain a sharp edge Crystallization: elements and compounds form crystals
ex. carbon can form diamonds and graphite which are used in machine parts and pencils Mixtures, Solutions, and Alloys They once again prove that the substance remains the same despite the change in shape
Mixtures can be classified as heterogeneous or homogeneous
ex. mixture of sand and water
Solutions involves one compound or element dissolving in another
ex. sugar dissolving in water
Alloys are a mixture of two or more metals
ex. brass is an alloy of copper and zinc Brass Instrument Applications 6CO2+6H2O+Light energy= C6H12O6+6O2 Photosynthesis:
Plants use take in carbon dioxide, water, and light energy to create glucose as a source of food Rusting of Iron
Rusting of iron is an example of oxidation
In this process iron (very reactive metal) combines with oxygen (when atmospheric moisture is present), creating iron oxides Fe+O2+=Fe2O3 Reactions in the Body C6H12O6+6O2=6CO2+6H2O+Energy (36 ATP) Aerobic Respiration
Whenever you move a chemical reaction occurs because the movement requires energy
When you inhale the oxygen breaks down glucose (energy source) creating carbon dioxide, water, and energy (ATP/adenosine triphosphate) C6H12O6=2CH5OH+2CO2+Energy Anaerobic Respiration
When you overexercise the body cells run out of oxygen
Lactic Acid is created which causes muscle cramps
Anaerobic respiration is also observed in bacteria, yeast, etc C3H8+5o2=4H2O+3CO2+Energy Batteries
Fireworks Other examples:
Propane grills (combustion reaction) Thank You
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