chemical reactions Sixth grade

What happens in a chemical reaction?

• Substances change in appearance but not in chemical composition.

• Substances change from solid to liquid or gas.

• Substances interact to form one or more new substances.

• New atoms are created or destroyed.

The reactants are

• the substances present when the reactions begins.

• the substances present when the reaction is complete.

• the properties that change after the reaction.

• the energy that is released or stored during the reaction.

In a synthesis reaction, the elements Fe and S might react to form which of the following?

• H_2​2

  ​​O

• FeS

• Na and Cl

• All of the above

In a decomposition reaction, NaCl might form which of the following?

• H_2​2

  ​​O

• FeS

• Na and Cl

• All of the above

In a chemical reaction, what happens to the total number of each type of atom?

• The total number of each type of atom always stays the same.

• The total number of each type of atom either increases or decreases.

• The total number of each type of atom always increases.

• The total number of each type of atom always decreases.

Identify the product(s) of the following reaction:

H_2​2

​​CO_3​3

​​ → H_2​2

​​O + CO_2​2

​​

• H_2​2

  ​​CO_3​3

  ​​

• H_2​2

  ​​ and O_3​3

  ​​

• H_2​2

  ​​O and CO_2​2

  ​​

• O and O_2​2

  ​​

In a science experiment, Marisa concludes that no chemical reaction has occurred. What evidence would support this conclusion?

• the mass and total number of atoms were conserved

• no energy was released

• a new element was created

• no new substance was formed

In a science experiment, Javi concludes that a chemical reaction has occurred. What evidence would support this conclusion?

• a substance melted

• a substance's color and odor changed

• a substance's mass and texture changed

• new atoms were created

In a science lab, burning steel wool creates only iron oxide. What must be true?

• The reaction of burning steel wool can sometimes create carbon monoxide.

• The reaction of burning steel wool will sometimes create iron oxide and water.

• The reaction of burning steel wool is not endothermic or exothermic.

• The reaction of burning steel wool always creates iron oxide.

True or false: In a chemical reaction, atoms of elements cannot be present in the products if they were not present in the reactants.

• True

• false