Designing a Safer Process: Hazard, Scale and Waste · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

When Small Reactions Grow Up

Science · Chemistry · ages 21-22
Name ______________________   Date ____________

  1. A rigid sealed vessel holds water and vapor, and no heat can escape. If you keep adding energy with an electric heater, both the temperature and the pressure inside will rise.

    Circle one:   True   False

  2. A reaction is routine in a flask but turns dangerous in a reactor. What changed?

    • The reaction equation stopped applying
    • The scale, because heat and pressure grow differently than volume
    • The purity of the starting materials

  3. A toxicity entry on a safety data sheet should change which gloves and ventilation you use.

    Circle one:   True   False

  4. Heat is made through the whole volume but escapes only through the walls. As the vessel grows, what happens?

    • Heat is trapped, because volume outgrows wall area
    • Heat escapes faster than it is made
    • Heat stops being made at all

  5. You swap a toxic solvent for a safer one. What defends the change?

    • The new solvent costs less per litre
    • The new solvent needs no handling rules at all
    • Evidence that the route still works just as well with the new solvent

  6. A sealed reactor holds a fixed amount of gas at 2.0 atm and 300 K. An exothermic reaction heats the gas to 450 K while the volume stays the same. When volume and amount of gas stay fixed, pressure is proportional to temperature. What is the new pressure, in atm?

    Answer: ______________

  7. A chemical plant builds a big spherical reactor that has exactly double the radius of a small test reactor. The reaction makes heat in proportion to the volume inside, and heat can only escape through the outer wall, in proportion to the wall area. Which statement is true?

    • The volume grows 8 times but the wall area grows only 4 times, so each square meter of wall has to remove twice as much heat.
    • The volume and the wall area both grow 8 times, so cooling stays just as easy.
    • The wall area grows 8 times while the volume grows 4 times, so cooling actually gets easier.
    • The volume and the wall area both grow 4 times, so nothing changes.

  8. A gram-scale exothermic step holds a steady temperature. The kilogram batch with the same cooling design keeps getting hotter. What is the best explanation?

    • The cooling jacket was fitted upside down
    • Impurities only appear at kilogram scale
    • The larger volume makes heat faster than the walls can release it

  9. A colleague says the kilogram batch is safe because the gram run never got hot and the ratios are unchanged. What is wrong?

    • Same ratios do not fix heat trapping, which depends on vessel size
    • Ratios never matter in chemistry
    • Small runs always hide their temperature

  10. Your process leaves wash water, leftover solvent, and solid filter cake. Which plan fits designing for the failure case?

    • Mix all three into one drum to save space
    • Recover the solvent, cut wash water use, and find a safer end for the cake
    • Store everything until the drums are full
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Answer key

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

When Small Reactions Grow Up W1-mt_5zhSYCYU_o-s1

  1. True · With a fixed volume and no heat loss, added energy has nowhere to go, so it shows up as higher temperature and then higher pressure.
  2. The scale, because heat and pressure grow differently than volume · The chemistry is unchanged. Size changes how heat and pressure build up, so scale-up needs its own design.
  3. True · That is the point of the sheet: each entry forces a handling choice.
  4. Heat is trapped, because volume outgrows wall area · Volume grows faster than wall area, so a bigger vessel releases heat more slowly than it makes it.
  5. Evidence that the route still works just as well with the new solvent · A substitution must keep the route working. Show the safer input does the same job.
  6. 3 · P2 equals P1 times T2 over T1, so 2.0 times 450 over 300, which is 3.0 atm.
  7. The volume grows 8 times but the wall area grows only 4 times, so each square meter of wall has to remove twice as much heat. · Volume grows with the radius cubed while area grows with the radius squared, so doubling the radius gives 8 times the heat but only 4 times the escape route.
  8. The larger volume makes heat faster than the walls can release it · Same chemistry, worse cooling per unit of mixture. Trapped heat speeds the reaction, which makes more heat.
  9. Same ratios do not fix heat trapping, which depends on vessel size · Ratios control chemistry, not cooling. Heat trapping is about size, so the small run cannot promise safety.
  10. Recover the solvent, cut wash water use, and find a safer end for the cake · Follow each stream and shrink it: recover what you can and make less of the rest.
Worksheet · LightMySky