Properties of Matter: Physical Changes vs. Chemical Changes Gr. 5 ... - Free Printable

Here are the solutions to the homework problems shown in the worksheets.

PREASSESSMENT

1. Identify Physical (P) or Chemical (C) Changes:
* a) Water boils on a stove: P (It is still water, just changing from liquid to gas).
* b) An old penny, lost in the grass, turns green: C (The metal reacts with air/moisture to form a new substance called patina).
* c) Fireworks explode in the night sky: C (Burning creates light, heat, and smoke; new substances are formed).
* d) Frost forms on a pumpkin: P (Water vapor freezes into ice; it is still water).
* e) An old Jack-O-lantern begins to rot: C (Decomposition changes the material into something new).

2. True (T) or False (F):
* a) Chemical changes happen only in things that are alive: F (Rusting iron and burning wood are chemical changes, but they aren't "alive").
* b) Physical changes happen only in things that are not alive: F (Melting ice cream or digesting food involves physical changes in living contexts).
* c) The way atoms are fastened together changes during a chemical change: T (Atoms rearrange to form new bonds).
* d) Atoms and molecules are both particles: T (They are the tiny building blocks of matter).
* e) If a material changes color, it is proof that a chemical change is happening: F (Adding red dye to white frosting changes the color, but it is just mixing, which is physical).

---

COMPREHENSION QUESTIONS

1. Multiple Choice:
* a) Which is the best sign that a chemical change is happening? B (flames). (Flames indicate burning/combustion, which creates new substances).
* b) How many of these changes are chemical changes? A (none).
* *Clouds forming:* Physical (water condensing).
* *Tomato rotting:* Chemical.
* *Plants making food:* Chemical (photosynthesis).
* *Wait, looking at the options:* The list has 3 items. Rotting and photosynthesis are chemical. Clouds are physical. That makes two chemical changes. So the answer is C.
* c) What kind of change is happening when water goes over a waterfall? B (a physical change only). (The water is moving and splashing, perhaps turning into mist, but it stays H₂O).

2. Fill in the blanks:
* a) Flames show a chemical change is taking place.
* b) Hydrogen and Oxygen react to form water.
* c) Chemical changes always change the way atoms are stuck together in molecules.
* d) Adding heat causes a material to change. If removing heat causes the material to return to the way it was, the change was probably a physical change.

---

SHORT ANSWER QUESTIONS

3. Explain using "atoms" and "molecules":
During a chemical change, the atoms inside the original molecules break apart and rearrange themselves. They stick back together in a different order to form brand new molecules, which creates a new material.

4. Describe a change that could be either:
Heating sugar.
* *Physical:* If you gently heat sugar, it might melt into a liquid syrup. If you cool it down, it hardens back into sugar candy.
* *Chemical:* If you heat it too much, it burns and turns black (carbon). You cannot turn the black ash back into white sugar.

5. Extensions and Applications (Kitchen Examples):

Three Physical Changes:
1. Melting Butter: Solid butter turns to liquid when heated. It is still butter and can be frozen back into a solid.
2. Chopping Vegetables: Cutting a carrot makes it smaller, but the pieces are still carrot.
3. Dissolving Sugar in Tea: The sugar disappears into the liquid, but if you boil the water away, the sugar crystals remain.

Three Chemical Changes:
1. Toasting Bread: The heat burns the surface of the bread, turning it brown and crunchy. You cannot turn toast back into soft white bread.
2. Baking a Cake: The batter ingredients (eggs, flour, baking powder) react with heat to rise and solidify. A baked cake cannot be turned back into raw eggs and flour.
3. Frying an Egg: The clear egg white turns white and solid when it hits the hot pan. This is a permanent change caused by heat altering the proteins.