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Combustion is an example of:
A) Physical Change
B) Chemical Change
Chemical Change
Complete the sentence: The law of conservation of mass states that ...
A) Mass can disappear
B) Mass and volume are properties of matter
C) matter is destroyed then replaced with something new
D) Matter is not created or destroyed, but can be rearranged into new substances.
D) Matter is not created or destroyed, but can be rearranged into new substances.
Which of the following represents a chemical change?
A) Stretching a rubber band
B) Toasting a piece of bread
C) An ice-block melting on a hot day
D) Cutting a shape of biscuit dough with a cookie cutter.
B) When bread it toasted a new product is formed.
Select an option that best completes the following sentence:
In a chemical reaction
A) some atoms disappearing
B) mixing substances together
C) the breaking and making of bonds
D) new atoms being created and making new bonds
C) Bonds are broken between atoms in the reactants, and once rearranged, the bonds are reformed, producing the products.
What type of change occurs when iron rusts?
Chemical change.
Is a substance changing colour always an example of physical or chemical change?
Neither - colour change can be a sign of physical or chemical change.
Which of the following statements in NOT correct?
A) Physical changes can be useful.
B) Physical changes are always reversible
C) There are 5 main indicators of physical change.
D) colour change can happen because of physical changes.
B) Physical change is often but not always reversible.
Which of the following observations would NOT be considered a sign of a chemical change?
A) noticing a solid forming
B) seeing a substance catch fire
C) cutting a solid into smaller pieces
D) seeing permanent colour change
C) Cutting a solid into smaller pieces.
Identify a chemical property of water:
A) Water is solid under 0 degrees
B) Water has a boiling point of 100 degrees
C) Solid water is less dense than liquid water
D) The bonds between atoms in water affects its reactivity.
D) all other options refer to physical properties.
What type of change occurs when ice melts into water? AND provide your reasoning.
Physical Change - the state is changing but the molecules/composition remain the same.
What is the difference between physical and chemical changes?
Physical changes do not break and/or form new bonds, which is how new substances form, whereas chemical changes do.
Define physical changes in your own words.
Physical change is when something changes in appearance but not in its chemical properties.
Identify the option that represents a chemical change and explain your answer:
A) XY --> XY
B) XX --> XX
C) YY --> YY
D) XY --> X + Y
D) XY were joined together in the reactants, X and Y are not bonded in the products
A student mixes two clear liquids and a yellow solid forms at the bottom. What kind of change is this, and how do you know?
Chemical change – the yellow solid is a new substance called a precipitate, which is evidence of a chemical reaction.
Watch the following video:
https://www.youtube.com/watch?v=Y_oppobHFzo
What kind of reaction is this? Justify your answer.
Chemical Change - A new substance (carbon dioxide gas) is formed. There’s bubbling/fizzing and the original substances are used up.
Why might only conducting 1 test/attempt at an experiment be considered poor scientific practice?
This is not good practice because it is likely that errors will occur during an experiment, and repeating the tests multiple times decreases their impact as the results can be averaged.
Why is a change of state (like freezing or boiling) considered a physical change?
Because no new substance (product) is formed; it's still the same substance in a different state (the particles are moving faster or slower)
What happens to bonds in chemical change? (Try using terms reactants and products)
The bonds in the reactant are broken, and new bonds are formed in the products.
A chemical coating can be applied to a carpenter's nail to delay the start of rusting. State the name of this reaction and explain how the coating can delay rusting.
Corrosion is a reaction that occurs between the surface of a substance with its environment. Iron corrodes easily with the oxygen and water in the air, so coating the iron nail in a non-corrosive paint will prevent this from happening as quickly.
What was the name of the scientist that introduced the law of conservation mass?
Antoine Lavoisier
Why is burning a candle both a physical and a chemical change? Explain both parts.
The wax melting is a physical change (change of state). The wax burning and producing light, heat, and new gases (like carbon dioxide) is a chemical change.
If salt dissolves in water and the mixture looks different, how can you prove it’s still a physical change and not a chemical one?
You can evaporate the water and recover the salt, showing that no new substance was created — just a mixture formed.
Stacey and Jess attended a birthday party. Stacey lit a sparkler and told Jess this was an example of physical change. However, Jess said it was a chemical change.
Who was correct? Using COBALT give an explanation as to what change occurred when the sparkler was lit.
Jess was correct, this was a chemical change. There were several signs of COBALT, including the formation of light, heat given off, and an odour produced indicating that new products had formed. In a physical change, no new products form.
After the chemical reaction lesson, two students wrote a summary sentence for their notes.
Student 1: 'We need to know the chemical properties of a substance we are using to make sure we use suitable protective equipment to preform the experiment with chemicals.
Student 2: 'We need to know the chemical properties of a substance, so we know which state it will be in when we use it.'
Identify which student's statement is most correct based on the chemical properties. Justify your response.
Student 1's statement is the most correct:
- predict chemical reaction from the chemical properties
- allows us to use control measures to avoid risk (e.g. safety gear).
Student 2's statement is incorrect:
- discusses physical properties rather than chemical properties of the substance.
Why can't most chemical changes be reversed by simple physical methods?
Because the original substances have been transformed into new ones with different properties; the atoms have rearranged.