Unit 6 4,5,6

Which statement best describes what happens during a chemical change?

• The chemical properties of a substance change, but its physical properties remain the same.
• ome properties of a substance change, but its identity remains the same.
• he physical properties of a substance change, but its chemical properties remain the same.
• Both the identity and the properties of a substance change.

Suppose that a substance in a beaker is heated over a burner in a science lab. Which observation would most likely indicate that a chemical change has occurred in the substance?

• If the substance is a liquid or solid, production of an odor would indicate a chemical change.
• If the substance is a liquid, a change of some of the liquid to gaseous form would indicate a chemical change.
• If the substance is a solid, a change of some of the solid to liquid form would indicate a chemical change.
• If the substance is a liquid or solid, an increase in temperature would indicate a chemical change.

Which event always involves a chemical change?

• conducting
• burning
• boiling
• melting
  

Which statement best describes a physical change?

• Changes can occur to certain chemical properties of the substance, but the overall shape of the substance will remain the same.
• hanges can occur to chemical properties of a substance, but the chemical composition of the substance remains the same.
• Changes can occur to physical properties of a substance, but the chemical composition of the substance remains the same.
• Changes can occur to certain physical properties of the substance, but the overall shape of the substance will remain the same.

Which laboratory activities involve chemical changes? Check all that apply.

• boiling saltwater for several minutes until only solid salt remains
• leaving a copper penny in vinegar until it turns green
• crushing a rock with a hammer to extract mineral deposits
• extracting iron filings from a sand mixture using a magnet

After Gerry mows his lawn, he often puts the grass clippings into his flower garden.How will this affect his garden?

• It will increase the amount of carbon in the soil and increase the amount of carbon dioxide released by decomposers.
• It will decrease the amount of carbon in the soil and decrease the amount of carbon dioxide released by decomposers.
• It will increase the amount of carbon in the soil and decrease the amount of carbon dioxide released by decomposers.
• It will decrease the amount of carbon in the soil and increase the amount of carbon dioxide released by decomposers.

Which characteristic of a substance is considered a chemical property?

• its conductivity
• its density
• its reactivity
• its boiling point

How is the nitrogen cycle important to humans?

• It produces free nitrogen that humans can breathe.
• It converts nitrogen into a form that humans can obtain by absorbing it through their skin.
• It produces nitrogen compounds that humans can breathe.
• It converts nitrogen into a form that humans can obtain by eating other organisms.

Cleo has a vegetable garden and wants to increase the amount of nitrogen in the soil.How can she most likely do this?

• harvest the vegetable plants continuously
• add several soybean plants to her garden
• reduce the number of decomposers that live in the soil
• decrease the amount of fertilizers she uses

Some bacteria live in the roots of plants like soybeans and peas.
What is the role of these bacteria in the nitrogen cycle?

• to break down nitrogen-containing compounds in dead organisms
  
• to absorb nitrogen-containing compounds from the soil
  
• to release free nitrogen into the atmosphere
  
• to convert free nitrogen into usable nitrogen