Which element has the same number of valence electrons as bromine (Br)?
(1 point)
krypton (Kr)
potassium (K)
chlorine (Cl)
selenium (Se)
Six.
burning wood
It is a physical change because there is no reaction.
The scientist used the Law of Conservation of Mass to predict that the product of the reaction would be 15.9 grams of copper sulfide. According to this law, mass is conserved in a chemical reaction, meaning that the total mass of the reactants is equal to the total mass of the products. By combining the masses of the copper and sulfur, the scientist could determine the expected mass of the copper sulfide product.
Sure! Let me simplify my response for a 7th grader level:
The scientist used a rule called the Law of Conservation of Mass to figure out that the product of the reaction would be 15.9 grams of copper sulfide. This rule says that during a chemical reaction, the total mass of the stuff you start with (reactants) is the same as the total mass of the stuff you end up with (products). By adding up the masses of the copper and sulfur, the scientist could guess how much copper sulfide would be made.
Of course! Here's a simpler explanation:
The scientist used a rule that says when you mix different things together, you can't make or lose any stuff. So, if you start with some copper and some sulfur, you'll end up with copper sulfide, and you won't have more or less stuff than before. By adding up the weights of the copper and sulfur, the scientist guessed how much copper sulfide would be made.
Chlorine (Cl) has the same number of valence electrons as bromine (Br).
Why are sodium (Na) and potassium (K) in the same group on the periodic table?(1 point)
Responses
They are both colorless.
They have similar reactivity.
They have similar atomic weights.
They are both hard and brittle.
They have similar reactivity.
A student cuts some fabric into two pieces. Is this change physical or chemical?(1 point)
Responses
It is a physical change because the process is reversible.
It is a physical change because there is no reaction.
It is a chemical change because there is no phase change.
It is a chemical change because the size changes.
It is a physical change because there is no reaction.
How are chemical changes different from physical changes?(1 point)
They involve heat.
They include shifts in the phase of matter.
They form new substances.
They are reversible.
They form new substances.
How does a balanced chemical equation demonstrate the Law of Conservation of Mass?(1 point)
Responses
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 all compounds remain bonded after 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.
Which procedure could be used to demonstrate that matter is conserved during a physical change?(1 point)
Responses
Find the mass of a cup of water. Boil the water. Find the mass of the water that remains.
Find the mass of a raw egg. Cook the egg. Find the mass of the cooked egg.
Find the mass of a piece of ice. Let the ice melt. Find the mass of the liquid water.
Find the mass of an apple. Cut the apple and remove the core. Find the mass of the remaining apple.
Find the mass of a piece of ice. Let the ice melt. Find the mass of the liquid water.
One molecule of bromine (Br2) and two molecules of potassium chloride (KCl) combine in a reaction. How many atoms are in the products?(1 point)
two
three
four
six
bot answer this
Which option is an example of a chemical change?(1 point)
Responses
folding paper
folding paper
chopping vegetables
chopping vegetables
stretching a rubber band
stretching a rubber band
burning wood
burning wood
bot answer this
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 there is no phase change.
It is a chemical change because there is no phase change.
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 the size changes.
bot answer this in 3 sentences
Use the chemical equation to complete the activity.
2Cu+S→Cu2S
2
Cu
+
S
→
Cu
2
S
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.