Question

the production of concrete requires cement. almost all cement is made by heating clay minerals and limestone together in a kiln, a type of oven that can reach high temperatures. the limestone contains calcium carbonate (caco₃). when limestone is heated to about 1,500°c, it breaks into carbon dioxide gas (co₂) and calcium oxide (cao), or quicklime. the chemical reaction below shows how quicklime is made. caco₃ → co₂ + cao select the true statements. low temperatures are required to make quicklime. carbon dioxide is produced when calcium carbonate breaks down. making quicklime is a chemical change. quicklime is used to make limestone.

Explanation:

1. The text states limestone is heated to about 1500°C to make quick - lime, so low temperatures are not required. This statement is false.
2. The chemical reaction $CaCO_3

ightarrow CO_2 + CaO$ shows that carbon dioxide is produced when calcium carbonate breaks down. This statement is true.

1. A chemical change occurs when a new substance is formed. Since calcium carbonate ($CaCO_3$) is transformed into carbon dioxide ($CO_2$) and calcium oxide ($CaO$) (quick - lime), making quick - lime is a chemical change. This statement is true.
2. The text describes limestone being used to make quick - lime, not the other way around. This statement is false.

Answer:

Carbon dioxide is produced when calcium carbonate breaks down.
Making quicklime is a chemical change.