7 Review day 5

81. Which is a reactant in this equation? R------------------------------------------------------------P

• NaOH
• H₂
• H₂O

82. What element has 4 atoms in the formula?

• Carbon (C)
• Nitrogen (N)
• Oxygen (O)

83. A student is watching firewood burn in a chimney. After some time he concludes that the matter is being destroyed by the chemical reaction because it appears that the wood is disappearing as it burns. Is the student correct?

• Yes. The wood is disappearing so its matter must be destroyed.
• No. The matter is simply changing into new compounds.

84. Is this chemical equation balanced?

• Yes, it is balanced.
• No, it is missing 2- H and has 1 extra O.

85. Which are examples of physical changes?

• Burning, bubbling and new odors
• Cutting, breaking and phase changes
• Color changes, cooking and baking

86. Which answer lists examples of chemical changes only? Read each very carefully.

• building a fire, making toast, breaking a pencil
• fireworks, baking a cake, digesting food
• cutting your hair, burning paper, melting ice cream

87. A person grabs a plastic object and observes that it is clear in color, odorless and solid. They then bend the object, hear a cracking sound and make the following observations: * object changed colors * object remained odorless * object began emitting light * object remained solid Pick the answer that provides the best reasoning for what happened.

• This is a chemical reaction because there was a change in color as well as light produced.
• This is a chemical reaction because the object remained solid and had no odor.
• This is a physical change because there was a change in color as well as light produced.

88. A student wants to conduct an experiment. They fill an ice tray with water and make the following observations: * water is liquid * water is odorless * water is colorless They place the ice tray in the freezer overnight and record the following observations: * the water is ice now * the water is solid * the water is odorless * the water is colorless Using the before and after observations, select an answer that best describes what happened.

• Chemical reaction because the water formed new chemical compounds.
• Physical change because the water froze and changed phases.
• Physical change because the water formed new chemical compounds.

89. A penny is placed on a table and the following observations are made: * it is shiny and brownish orange * it is round * it has a metallic smell A drop of acid is placed on the penny and the following observation are made: * it is greenish blue * it is smaller and irregularly shaped * a brown, foul smelling vapor was produced Using the before and after observations, select an answer that best describes what happened.

• Chemical reaction because it only changed shape.
• Physical change because it only changed shape.
• Chemical reaction because it changed color and produced a gas.

90. Which is a type of a chemical reaction?

• Ice Melting
• Nails Rusting
• Rock Breaking