The four states of matter and particle motion

Answer Key - Grade 10 Science Worksheet

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

1. 1.

   Ari heats 50 g of ice at −20 °C until it is liquid water at 0 °C. Ice warms at 2.09 J/g/°C; melting takes 334 J/g. How many joules?

   18,790 J
2. 2.

   Bo heats 100 g of ice at −15 °C until it is liquid water at 0 °C. Ice warms at 2.09 J/g/°C; melting takes 334 J/g. How many joules?

   36,535 J
3. 3.

   Esme heats 200 g of ice at −5 °C until it is liquid water at 0 °C. Ice warms at 2.09 J/g/°C; melting takes 334 J/g. How many joules?

   68,890 J

4. Read this first

   Energy added to 100 g of H₂O (computed from standard values)

   energy added (kJ)	temperature (°C)	state
   0	−20	ice
   4.2	0	ice
   20.9	0	ice and water
   37.6	0	water
   58.5	50	water
   79.4	100	water
   192.4	100	water and steam
   305.4	100	steam

5. 4.

   From 79.4 to 192.4 kJ the temperature stays at 100 °C while the energy keeps rising. What does the energy do, Jun?

   • It breaks the water molecules into separate hydrogen and oxygen atoms
   • It pulls molecules apart into a gas, raising their potential energy, not their speed
   • It speeds the molecules up, but the thermometer cannot read above 100 °C while boiling
6. 5.

   Boiling the 100 g takes 226 kJ, but melting it took only 33.4 kJ. Why is boiling so much larger, Kira?

   • Water molecules become much heavier as steam, so each needs more energy to move
   • Boiling also raises the temperature by 100 °C, which costs most of the extra energy
   • Boiling separates molecules completely; melting only loosens their fixed pattern
7. 6.

   Compare energy per °C for liquid water and for ice in the table. What do you find, Luz?

   • Water takes about twice as much: 0.42 kJ per °C against 0.21
   • They take the same amount, because both are H₂O
   • Ice takes more, because a solid is harder to heat than a liquid
8. 7.

   One gas is heated from 300 K to 600 K. What happens to the share of fast molecules, Noah?

   • The slowest molecules disappear, so the ones left are fast
   • The molecules speed up by the same amount, so the spread stays the same
   • A larger share moves faster than any given speed, though some stay slow
9. 8.

   A sealed balloon shrinks in a freezer. Using the particle model, why, Pia?

   • The cold air outside pushes harder on the balloon's walls than it did before
   • The molecules themselves shrink when they get cold, so they take up less room
   • Colder molecules hit the walls less often and less hard, so they push in less
10. 9.

    Water boils at about 95 °C in Denver, not 100 °C. Why, Tala?

    • Gravity is weaker there, so the water is lighter and heats up sooner than elsewhere
    • Denver has less oxygen, so the water burns at a lower temperature than at sea level
    • Air pressure is lower there, so molecules escape the liquid at a lower temperature
11. 10.

    Wet laundry dries at 20 °C, far below water's boiling point. Why, Zee?

    • The cloth heats the water to 100 °C a little at a time, step by step
    • A few fast surface molecules escape even though the average speed is low
    • At 20 °C each molecule is fast enough to escape, so the cloth dries at once