Reaction Dynamics: Trajectories Across a Potential Energy Surface · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

When molecules ignore the expected path

Science · Chemistry · ages 23-24
Name ______________________   Date ____________

  1. What sits at the very top of the barrier pass?

    • The transition state, half broken and half formed
    • The unreacted mixture
    • The stable product

  2. Why do most molecular collisions cause no reaction?

    • The molecules never truly touch
    • They lack the energy or the orientation needed
    • The barrier moves away

  3. Heating a mixture speeds reaction because more molecules can clear the barrier.

    Circle one:   True   False

  4. Many trajectories reach the top but fall back to reactants. What does this do?

    • Lowers the true rate below the barrier prediction
    • Leaves the rate unchanged
    • Raises the true rate above prediction

  5. Two reactions differ only in barrier height. Which runs slower?

    • The one with the lower barrier
    • They run at equal rates
    • The one with the higher barrier

  6. What does the orientation requirement explain?

    • Why heat matters
    • Why fast collisions can still fail when wrong ends touch
    • Why barriers exist

  7. A product ratio set by downhill shape rather than barrier heights supports statistical control.

    Circle one:   True   False

  8. The measured product ratio contradicts the computed barriers. What should you inspect?

    • The reactant purity only
    • The room lighting
    • The surface shape after the transition state
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Answer key

For grown-ups. Fold this page away before handing over the rest.

When molecules ignore the expected path W1-mt_6ctTUYqYtS-s1

  1. The transition state, half broken and half formed · The top holds the fleeting half-and-half arrangement.
  2. They lack the energy or the orientation needed · Only energetic, well-aimed hits climb the pass.
  3. True · Faster molecules clear the climb more often.
  4. Lowers the true rate below the barrier prediction · Recrossers were counted as products but never arrive.
  5. The one with the higher barrier · Higher barriers admit fewer energetic collisions.
  6. Why fast collisions can still fail when wrong ends touch · Energy alone cannot rescue a mis-aimed hit.
  7. False · That signature points to dynamic, not statistical, control.
  8. The surface shape after the transition state · Downhill steering can skip the expected valley and set the ratio.
Worksheet · LightMySky