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. carbon dioxide is produced when calcium carbonate breaks down. quicklime is used to make limestone. low temperatures are required to make quicklime. making quicklime is a chemical change.

Explanation:

• From the chemical reaction $CaCO_{3}

ightarrow CO_{2}+CaO$, carbon - dioxide is a product when calcium carbonate decomposes, so the first statement is true.

• Limestone breaks down to form quicklime, not the other way around, so the second statement is false.
• High temperatures (about $1500^{\circ}C$) are required to make quicklime, not low temperatures, so the third statement is false.
• Making quicklime involves a chemical reaction where a new substance (quicklime) is formed from another substance (calcium carbonate), so it is a chemical change, and the fourth statement is true.

Answer:

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