Which element has the same number of valence electrons as bromine (Br)?
(1 point)
Responses
krypton (Kr)
krypton (Kr)
chlorine (Cl)
chlorine (Cl)
potassium (K)
potassium (K)
selenium (Se)
chlorine (Cl)
Why are sodium (Na) and potassium (K) in the same group on the periodic table?(1 point)
Responses
They are both hard and brittle.
They are both hard and brittle.
They have similar reactivity.
They have similar reactivity.
They have similar atomic weights.
They have similar atomic weights.
They are both colorless.
They have similar reactivity.
Which option is an example of a chemical change?(1 point)
Responses
stretching a rubber band
stretching a rubber band
folding paper
folding paper
chopping vegetables
chopping vegetables
burning wood
burning wood
A student cuts some fabric into two pieces. Is this change physical or chemical?(1 point)
Responses
It is a physical change because there is no reaction.
It is a physical change because there is no reaction.
It is a chemical change because the size changes.
It is a chemical change because the size changes.
It is a physical change because the process is reversible.
It is a physical change because the process is reversible.
It is a chemical change because there is no phase change.
It is a physical change because there is no reaction.
How are chemical changes different from physical changes?(1 point)
Responses
They involve heat.
They involve heat.
They are reversible.
They are reversible.
They include shifts in the phase of matter.
They include shifts in the phase of matter.
They form new substances.
They form new substances.
Chemical Change Unit Test
6 of 76 of 7 Items
Question
How does a balanced chemical equation demonstrate the Law of Conservation of Mass?(1 point)
Responses
it shows that all compounds remain bonded after the reaction
it shows that all compounds remain bonded after the reaction
it shows that only physical changes follow the Law of Conservation of Mass
it shows that only physical changes follow the Law of Conservation of Mass
it shows that no atoms have been gained or lost during the reaction
it shows that no atoms have been gained or lost during the reaction
it shows that the properties of the elements stay the same after the reaction
it shows that no atoms have been gained or lost during the reaction
Use the chemical equation to complete the activity.
2Cu+S→Cu2S
Copper (Cu) reacts with sulfur (S) to form copper sulfide as shown in the equation. A scientist adds 12.7 grams of Cu to 3.2 grams of S to start the reaction. In this reaction, all of the copper and all of the sulfur react. Before running the experiment, the scientist expected the products of the reaction will be a total of 15.9 grams of copper sulfide (Cu2S). In 1–2 sentences, explain the law that the scientist used to predict that the product of the reaction would be 15.9 grams of copper sulfide.
(2 points)