The four states of matter and particle motion

Answer Key - Grade 10 Science Worksheet - Challenge Me

Circle the best answer, or write your answer on the line.

1. 1.

   Ari turns 10 g of ice at −10 °C into steam at 100 °C. Specific heats: ice 2.09, water 4.18 J/g/°C. Melting 334 J/g, boiling 2260 J/g. Total joules?

   30,329 J
2. 2.

   Bo turns 5 g of ice at −20 °C into steam at 100 °C. Specific heats: ice 2.09, water 4.18 J/g/°C. Melting 334 J/g, boiling 2260 J/g. Total joules?

   15,269 J
3. 3.

   Esme turns 20 g of ice at −5 °C into steam at 100 °C. Specific heats: ice 2.09, water 4.18 J/g/°C. Melting 334 J/g, boiling 2260 J/g. Total joules?

   60,449 J
4. 4.

   Kira drops 20.0 g of ice at 0 °C into 200 g of water at 25 °C. Melting takes 334 J/g; water 4.18 J/g/°C. What is the final temperature?

   • About 15.5 °C, after the water melts the ice and warms the meltwater
   • About 12.5 °C, the simple average of the two starting temperatures, 0 °C and 25 °C
   • About 22.7 °C, found by skipping the energy needed to melt the ice
5. 5.

   Dry ice (solid CO₂) turns straight to gas at 1 atm and never forms a puddle. CO₂'s triple point is 5.1 atm. Why no liquid, Luz?

   • CO₂ molecules are too light to stay together as a liquid anywhere on Earth
   • Liquid CO₂ needs more than 5.1 atm; at 1 atm the solid goes straight to gas
   • Dry ice is so cold that no liquid can form at any pressure whatever

6. Read this first

   Water and ice at 0 °C (real data, CRC)

   material	density (g/cm³)
   liquid water	0.9998
   ice	0.9167

7. 6.

   Milo says ice floats because ice molecules are lighter than liquid water molecules. Verdict?

   • No: the molecules are identical; ice's open pattern spreads them out, lowering density
   • Yes: a lower density means each ice molecule has less mass than a water molecule
   • No: ice floats because it is colder, so its molecules have less kinetic energy
8. 7.

   Noah says a tub of 30 °C water holds less thermal energy than a cup of 60 °C water, since 60 is hotter. Verdict?

   • Wrong: both are water, so the two samples hold equal amounts of thermal energy
   • Right: a higher temperature always means more thermal energy in a sample
   • Not necessarily: temperature is only an average, and the tub has far more particles
9. 8.

   NH₃ (17.0 u) and HCl (36.5 u) gases start from opposite ends of a long tube at one temperature. Where does white NH₄Cl form, Ren?

   • Closer to the HCl end, since lighter NH₃ moves about 1.5 times as fast
   • At the midpoint, since both gases carry the same average kinetic energy
   • Closer to the NH₃ end, since ammonia is the more reactive gas
10. 9.

    Why does sweating cool the body, Tala?

    • The fastest molecules escape, so the sweat left behind has lower average energy
    • Sweat soaks up cold from the surrounding air as it slowly evaporates off the skin
    • The molecules slow down together as they leave the skin, and that cools it down
11. 10.

    In a sealed jar at 25 °C, water and its vapor are in equilibrium. What does that mean, Zee?

    • Molecules evaporate and condense at equal rates, so amounts stay steady
    • Evaporation keeps running faster than condensation until the water is gone
    • Evaporation has stopped, so the jar holds just still water