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Question 1

Which of these is a physical change?

Iron rusting in the rain
A candle burning down
Ice melting into water
Bread turning moldy

Question 2

Which of these is a chemical change?

Tearing a piece of paper
Dissolving sugar in water
Bending a paperclip
A firework exploding with light, sound, and new gases

Question 3

According to PS.8.1.4, which category of change includes size, shape, and state?

Physical change
Chemical change
Nuclear change
Both physical and chemical equally

Question 4

Which of these is NOT one of the evidence categories for a chemical change named in the standard?

A change in energy
A change in color
A change in mass with nothing added or removed
Formation of a gas or precipitate

Question 5

A student mixes two clear liquids and a cloudy solid forms and settles to the bottom. What is this solid called, and what does it show?

A solute; it shows the liquids dissolved into each other
A precipitate; it shows a chemical change occurred
A precipitate; it shows a physical change occurred
A catalyst; it shows the reaction sped up

Question 6

Baking soda and vinegar are combined in a balloon-tipped bottle, and the balloon inflates. What evidence of a chemical change is this?

A change in state only
Formation of a gas
A change in shape
Formation of a precipitate

Question 7

Which pair correctly matches a physical change with a chemical change?

Physical: crushing a can. Chemical: cutting paper.
Physical: freezing water. Chemical: burning wood.
Physical: rusting iron. Chemical: boiling water.
Physical: baking a cake. Chemical: dissolving salt.

Question 8

You dissolve sugar in warm water and it disappears. Later, you boil away all the water and see sugar crystals again. What does this show?

A chemical change occurred, because a new substance appeared
A physical change occurred, because the sugar can be recovered unchanged
Mass was destroyed when the sugar dissolved
The sugar reacted with the water to form a gas

Question 9

A nail left outside slowly develops a reddish-brown flaky coating. What kind of change is rusting, and why?

Physical, because the nail's shape does not change
Chemical, because iron reacts with oxygen to form a new substance (iron oxide)
Physical, because rust can be scraped off
Chemical, because the nail gets smaller

Question 10

Which change in energy is most closely associated with evidence of a chemical reaction?

The temperature stays exactly the same the whole time
The mixture suddenly feels much hotter or colder as the reaction proceeds
The object changes shape when squeezed
The object becomes see-through

Question 11

Melting, freezing, boiling, condensing, and dissolving are all examples of which kind of change?

Chemical changes
Nuclear changes
Physical changes
Irreversible changes only

Question 12

A student burns a piece of paper and is left with a small amount of ash, weighing much less than the original paper. Is mass conserved in this reaction?

No, mass was destroyed by the fire
Yes, but only some of the products (gases and water vapor) escaped into the air, so the total mass, including those, is conserved
No, because chemical reactions always lose mass
Yes, because the ash weighs exactly what the paper weighed

Question 13

The Law of Conservation of Mass states that in a chemical reaction:

Mass can be created but never destroyed
The total mass of the reactants equals the total mass of the products
Atoms are destroyed and replaced with new ones
The number of molecules stays exactly the same

Question 14

During a chemical reaction, what actually happens to the atoms of the reactants?

They are destroyed and new atoms are created
They disappear and reappear as energy
They are rearranged into new combinations to form the products
They stay bonded exactly as they were

Question 15

In the balanced equation 2H2 + O2 -> 2H2O, what does the coefficient "2" in front of H2 tell you?

There are 2 hydrogen atoms in one molecule of H2
There are 2 molecules of H2 reacting
The reaction produces 2 grams of hydrogen
The reaction happens twice as fast

Question 16

The unbalanced equation Fe + O2 -> Fe2O3 needs coefficients so the number of atoms matches on both sides. Which set of coefficients balances it?

1 Fe + 1 O2 -> 1 Fe2O3
2 Fe + 3 O2 -> 2 Fe2O3
4 Fe + 3 O2 -> 2 Fe2O3
3 Fe + 2 O2 -> 1 Fe2O3

Question 17

Why must a chemical equation be balanced?

So the equation looks neat and symmetrical
So the same number of each type of atom appears on both sides, supporting the Law of Conservation of Mass
So the reaction happens faster
So the products have less mass than the reactants

Question 18

A reaction takes place inside a sealed, rigid container (a closed system). A student weighs the container before and after the reaction. What should they find?

The container weighs less after, because gas escaped
The container weighs the same before and after
The container weighs more after, because new mass was created
The weight cannot be predicted without knowing the chemicals

Question 19

Why does an open-system reaction (like a fire in open air) appear to lose mass, even though mass is truly conserved?

Because atoms are actually destroyed in open systems
Because some products (often gases) escape into the surroundings and are not weighed
Because the Law of Conservation of Mass does not apply outdoors
Because open systems always involve less matter to begin with

Question 20

In the equation CH4 + 2O2 -> CO2 + 2H2O, how many total oxygen atoms are on the reactant side?

2
3
4
6

Question 21

A model shows 4 red spheres (reactant A) and 4 blue spheres (reactant B) combining into 4 purple two-sphere molecules (product AB). Does this model support the Law of Conservation of Mass?

No, because a new color (purple) appeared
Yes, because the same number of red and blue spheres (atoms) exist before and after, just rearranged
No, because the reactants disappeared
Cannot tell without knowing the actual mass in grams

Question 22

Which statement correctly connects physical/chemical change (PS.8.1.4) to conservation of mass (PS.8.1.5)?

Mass is only conserved during physical changes, not chemical changes
Mass is conserved during both physical and chemical changes, because atoms are neither created nor destroyed in either case
Mass is only conserved during chemical changes
Mass conservation only applies to changes of state

Question 23

A student says, "When wood burns, it just disappears." Using conservation of mass, what is the best correction?

The student is correct, the wood's atoms are truly gone
The wood's atoms combined with oxygen to form gases (like carbon dioxide and water vapor) and ash, which together have the same total mass as the wood and oxygen that reacted
The wood turned entirely into light and heat, which have mass
The fire destroyed a small amount of the wood's mass permanently

Question 24

Which piece of evidence, if observed during a reaction in a beaker, would most strongly suggest a chemical change rather than a physical one?

The liquid changes from clear to bright yellow and bubbles form
The liquid gets colder because it was placed in a freezer
The liquid is poured from one container to a smaller one
The liquid's surface ripples when stirred

Question 25

The equation N2 + 3H2 -> 2NH3 is already balanced. If you started with 28 grams of N2 and 6 grams of H2, and the reaction used all of both, what must the mass of the NH3 produced be?

Less than 34 grams, because some mass was lost as heat
Exactly 34 grams, the sum of the reactant masses
More than 34 grams, because new atoms were created
Impossible to know without a scale

Science 8 Unit Test: Changes in Matter

Unit Test