Solids, liquids and gases as moving particles

Answer Key - Grade 8 Science Worksheet - Challenge Me

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

1. Read this first

   Melting test (example data)

   trial	mass of ice (g)	minutes to melt
   A	400	8
   B	100	2

   All of the hot plate's energy goes into melting.

2. 1.

   Each minute the hot plate adds the same energy, all of it melting ice at 0 °C. How many minutes will 200 g of ice take, Ari?

   4 minutes
3. 2.

   Each minute the hot plate adds the same energy, all of it melting ice at 0 °C. How many minutes will 600 g of ice take, Bo?

   18 minutes
4. 3.

   A hot plate adds the same energy each minute, all of it melting ice at 0 °C. How many minutes will 100 g of ice take, Esme?

   3 minutes
5. 4.

   Under a microscope, specks of smoke in a sealed cell of still air jiggle in random directions. What explains this, Jun?

   • The specks swell and shrink as the air around them warms and cools, so they seem to jiggle about
   • Unseen air particles, moving fast in every direction, keep bumping the specks from different sides
   • Air particles are at rest, and just the smoke specks have energy to move about on their own
   • A steady breeze through the cell pushes the specks around, which makes them seem to jiggle at random
6. 5.

   A hot metal spoon sits in cool water. After a few minutes both are at one temperature. What explains this, Luz?

   • Heat leaves the spoon until the spoon is cold, while the water stays at its first temperature
   • Cold flows from the water into the spoon until both are equally cool, much as water flows into a cup
   • Faster spoon particles pass energy to slower water particles in collisions until the speeds match
   • The spoon's particles stop moving and hand their energy over to the water particles around them

7. Gas in a flexible balloon (example data)

   temperature (°C)	volume (mL)
   0	500
   20	537
   40	573

8. 6.

   Milo says the gas volume doubles when the temperature doubles from 20 °C to 40 °C. Does the table support that?

   • No: a gas should not change volume when its temperature changes
   • No: the volume rose only from 537 mL to 573 mL, much less than double
   • Yes: 40 °C is twice 20 °C, and 573 mL is more than twice 537 mL
   • Yes: the volume rose each time the temperature rose, so it must have doubled

9. Dye test, three trials at each temperature (example data)

   trial	seconds at 50 °C	seconds at 10 °C
   1	38	95
   2	45	110
   3	41	90

10. 7.

    Noah compares the dye times. Which statement do the data support?

    • The 50 °C times range from 38 s to 45 s, so these data are too uneven to trust for a comparison
    • The two sets of times overlap, so temperature made no real difference to the dye
    • Every 50 °C trial was faster than every 10 °C trial, a gap far larger than the spread within a group
    • The 110 s trial is far from the others, so it should be thrown out before the two groups are compared
11. 8.

    Each beaker started with 200 mL of water. Pia compares the mass lost from open beakers in 24 hours. Which statement do the data support?

    • The 4 g result is the odd one in its group, so it should be removed before the groups are compared
    • The 10 °C losses range from 2 g to 4 g, so these data are too uneven to support any comparison
    • Each 50 °C beaker lost more than any 10 °C beaker, a gap much larger than the spread within either group
    • Evaporation depends on the beaker and not on the water temperature, so these data show nothing about the effect of warmth
12. 9.

    Dry ice (solid carbon dioxide) shrinks in an open bowl and leaves no liquid. Which explanation fits the particle model, Ren?

    • A liquid forms first, but it evaporates too quickly for anyone to see it on the bottom of the bowl
    • Its particles gain enough energy to leave the solid and spread out as a gas without forming a liquid
    • Its particles shrink as the dry ice warms until they are far too small to see, so the solid vanishes
    • Its particles are destroyed as the dry ice warms, so just the empty bowl is left behind in the room
13. 10.

    Drops form on the outside of a cold glass of water. Which explanation fits the particle model, Tala?

    • Water vapor particles in the air lose energy on the cold glass, slow down, and condense into a liquid
    • The cold glass creates new water particles from the air that touches it, which adds mass to the glass
    • Water seeps through tiny holes in the glass from the inside, and the drops are the water that got through
    • Cold particles from the glass spread into the air and freeze the water vapor into small drops there