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For 2Cl(g)→Cl₂(g), state the signs of ΔH and ΔS.
Bond formation releases energy, so enthalpy falls. Two freely moving atoms become one molecule, reducing the number of particles and disorder.
ΔH
Explain a polar covalent bond using a suitable example.
When bonded atoms have unequal electronegativities, the shared pair shifts toward the more electronegative atom, producing partial charges without complete electron transfer.
Hδ⁺–Clδ⁻ is polar covalent because Cl attracts the shared pair more strongly.
List the factors that cause main-group ionisation enthalpy to decrease down a group.
Each step down adds a shell, increases atomic size and increases shielding. These effects reduce attraction between the nucleus and the valence electron, outweighing the increased nuclear charge.
Larger size and stronger shielding reduce ionisation enthalpy down a group.
For hydrogen with ground-state energy −2.18×10⁻¹¹ erg, calculate the energy needed for
Use the Bohr energy difference. One erg equals 10⁻⁷ J.
Write 0.0048, 234000, 8008, 500.0 and 6.0012 in scientific notation.
Move the decimal point so that one non-zero digit remains before it; the number of places moved gives the power of ten.
Sitar string A is 324 Hz and beats at 6 Hz with B. Slightly reducing A's tension reduces beats to 3 Hz. Find B's frequency.
Principle and reasoning. Work from the governing physical relation and apply it to every stated part.
Reducing tension lowers A's frequency. Since this initially brings the frequencies closer, B must lie below 324 Hz.
Earth's escape speed is \(11.2\,\mathrm{km\,s}\)⁻¹. A body is launched at three times this speed. Find its speed very far from Earth.
Conserve mechanical energy, using vₑ²=2GM/R.
A \(1.5\,\mathrm{m}\) pendulum is released from the horizontal and loses 5% of its initial energy to air resistance. Find its speed at the lowest point, taking \(g=9.8\,\mathrm{m\,s}\)⁻².
The drop in height equals the string length. The remaining 95% of mgl becomes kinetic energy.
Two \(0.050\,\mathrm{kg}\) billiard balls approach in opposite directions at \(6.0\,\mathrm{m\,s}\)⁻¹ and rebound with unchanged speed. Find the impulse on each ball.
For either ball, the velocity reverses. Impulse equals the change in momentum.
For y²=−8x, give
Translate every condition into an equation and retain exact values throughout the conic calculation.
The last line satisfies the original conditions and supplies every requested part.