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c101_f10_1110 - Additional notes on Hesss Law 1 Hf(element...

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Additional notes on Hess’s Law 1. Δ H f ° (element, most stable form) = 0 kJ/mol Examples : C(s, graphite), O 2 (g), H 2 (g) => Δ H f ° = 0. Not C(s, diamond), O 3 (g), H(g). 2. Δ H rxn = ΣΔ H f ° (products) – ΣΔ H f ° (reactants) Can be asked to solve for Δ H rxn , Δ H f ° of a product, or Δ H f ° of a reactant. 3. Δ H rxn = Δ H 1 + Δ H 2 + Δ H 3 Can be asked to solve for Δ H rxn , Δ H 1, etc.
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Chemistry 101 Fall 2010 2 Light and radiation Light is a type of electromagnetic (EM) radiation, and light has energy. Many kinds of light exist. Ultraviolet (UV) light causes skin to tan or burn. Infrared (IR) light is used in heat lamps and remote controls. Visible light has energy between UV and IR. Some types of light and EM radiation have more energy and cause more damage than other types. Examples : UV light/radiation vs. IR light, X-rays vs. radio waves
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Chemistry 101 Fall 2010 3 Light and EM radiation have features of waves. (Figs. 7-1, 7-2) Frequency ( ν ) : “nu”, the number of wave crests (peaks) that pass a fixed point in space in one second. Units are “per second” = 1/s = 1 s -1 . Also, known as Hertz (Hz), 1 Hz = 1/s. Wavelength ( λ ) : “lambda”, the distance between wave peaks. Units are in length, such as meters or nm (nanometers). Amplitude : the height of a wave, often measured from peak to trough, sometimes measured from peak to baseline. Also known as intensity , the brightness of a light source.
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Chemistry 101 Fall 2010 4 For all waves, wavelength x frequency = speed of wave λ x ν = speed.
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