Exam 2B-09Practice

# 0 moles of hydrogen atoms emit the photons for this

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What is the energy needed to make 8.0 moles of hydrogen atoms emit the photons for this problem? ( N A = 6.022×10 23 objects·mol -1 ) 2. (6 pts) Calculate the DeBroglie wavelength of a proton moving at 2.00×10 5 m∙s -1 . ( m p = 1.67×10 -27 kg) Page 1 of 3

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3. (6 pts) What is the minimum uncertainty in the position of a photon if the uncertainty in the momentum is 3.000×10 -30 kg∙m∙s -1 ? 4. (18 pts) We will be applying Hess’s law to ionic bonding. The Born-Haber method is how you determine enthalpies of formation for salts. Rb(g) + 1/2Br 2 (g) → RbBr(s) a) Calculate the enthalpy of formation of rubidium bromide from gaseous elements using the following known standard enthalpies: Rb(g) → Rb + (g) + e - ΔH I = 403 kJ Br 2 (g) → 2Br(g) ΔH D = 193 kJ Br - (g) → Br(g) + e - ΔH EA = 325 kJ RbBr(s) → Rb + (g) + Br - (g) ΔH U = 668 kJ b) What type of reaction is the formation of RbBr: exothermic endothermic c) What is the ΔH f for Br 2 since it is in its standard state? d) The last reaction ( ΔH U = 668 kJ·mol -1 ) is determined by subliming a salt into a plasma by using the heat lost to sublimation from a 75.0 mole heated aluminum block. If 0.170 moles of rubidium bromide are sublimed by the block, what is the final temperature of the block if the initial temperature is 1300.0°C? ( C p, Al = 25.11 J·mol -1 ·K -1 ) 2
5. (6 pts)
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• Fall '08
• COLLIER
• Atom, Mole, Excited state, ground state, methane gas

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