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An equilibrium constant is Kc=[NH₃]⁴[O₂]⁵/([NO]⁴[H₂O]⁶). Give the balanced gaseous equation represented by this expression.
Numerator species are products and denominator species are reactants; exponents give stoichiometric coefficients.
4NO(g)+6H₂O(g) ⇌ 4NH₃(g)+5O₂(g).
For N₂+3H₂→2NH₃, ΔrH°=−92.4 kJ mol⁻¹. Find ΔfH° of NH₃(g).
Elements in standard states have zero formation enthalpy. The reaction forms two moles of ammonia.
−46.2 kJ mol⁻¹.
Describe the resonance contributors of SO₃, NO₂ and NO₃⁻.
Shift only π electrons and formal charges while preserving the atomic skeleton. Equivalent positions generate equivalent contributors; the observed bonds have intermediate orders.
SO₃ has three equivalent S–O contributors, NO₂ has two main N–O contributors, and NO₃⁻ has three equivalent contributors.
Explain why a cation is smaller and an anion larger than its parent atom.
Electron loss reduces repulsion and may remove the outer shell; the remaining electrons feel greater effective attraction per electron. Electron gain increases electron-electron repulsion while nuclear charge stays fixed.
Calculate the wavelength emitted by hydrogen for the transition n=4 to n=2.
Apply the Rydberg relation for an emission transition.
At sea level, the mass of the air column above 1 cm² is \(1034\,\mathrm{g}\). Calculate the pressure exerted by this air column in pascals.
Pressure is force per area. Convert mass to kilograms and area to square metres, then use weight mg as the force.
A \(2.5\,\mathrm{kg}\) copper block at 500°C is placed on ice at 0°C. Find the maximum ice melted; c꜀ᵤ=0.39 J g⁻¹ K⁻¹ and L_f=335 J g⁻¹.
Principle and reasoning. Work from the governing physical relation and apply it to every stated part.
The copper cools to 0°C. Its lost heat melts ice without changing the ice-water temperature.
Estimate the Sun's mass using Earth's mean orbital radius 1.5×10¹¹ m and period 365.25 days.
Equate gravitational force to the centripetal force of Earth's nearly circular orbit.
A \(70\,\mathrm{kg}\) person stands on a scale in a lift. Give the scale readings for: constant upward speed, downward acceleration \(5\,\mathrm{m\,s}\)⁻², upward acceleration \(5\,\mathrm{m\,s}\)⁻², and free fall. Take \(g=10\,\mathrm{m\,s}\)⁻².
The scale reading in kilograms is the normal reaction divided by g.
A cricketer can throw a ball to a maximum horizontal range of \(100\,\mathrm{m}\). How high can the same ball be thrown vertically?
For a fixed launch speed, the maximum horizontal range is obtained at 45°. Use that result to find the speed, then use it for a vertical throw.