11. when powdered iron is left exposed to the air, it rusts. explain why the mass of the rust is greater than the mass of the powdered iron.
12. a change in odor can also be a clue that a chemical change has occurred. describe at least one situation in which you might be likely to detect such a change in odor in the kitchen.
classify each of these statements as always true, at; sometimes true, st; or never true, nt.
13. ______ a physical change is reversible.
14. ______ in a chemical reaction, reactants are changed into products.
15. ______ the amount of matter present appears to change during a chemical reaction.
16. ______ matter can be created during a chemical reaction.
17. ______ the substances formed in a chemical reaction are called reactants.

Question

Accepted Answer

### Question 11
# Brief Explanations:
Rusting is a chemical reaction where iron ($\ce{Fe}$) reacts with oxygen ($\ce{O_2}$) and water ($\ce{H_2O}$) from the air. The reaction is typically represented as $\ce{4Fe + 3O_2 + 6H_2O -> 4Fe(OH)_3}$, and then $\ce{Fe(OH)_3}$ can further react to form rust (like $\ce{Fe_2O_3\cdot nH_2O}$). According to the law of conservation of mass, the mass of the products (rust) is equal to the mass of the reactants (iron, oxygen, and water). Since oxygen and water from the air are added to the iron during rusting, the mass of the rust (which includes the mass of iron plus the mass of the oxygen and water that reacted with it) is greater than the mass of the original powdered iron.
# Answer:
Rusting is a chemical reaction where iron reacts with oxygen and water from the air. By the law of conservation of mass, the mass of rust (products: iron + oxygen + water) is greater than the mass of powdered iron (reactant) because oxygen and water are added during the reaction.

### Question 12
# Brief Explanations:
One situation in the kitchen is the spoilage of milk. Fresh milk has a mild, slightly sweet odor. When milk undergoes a chemical change (spoilage, due to the action of bacteria or enzymes), it starts to produce lactic acid or other compounds, and the odor changes to a sour smell. Another example is cooking eggs: raw eggs have a certain odor, but when they are cooked (a chemical change, denaturation of proteins), the odor changes, often becoming more "cooked" or slightly sulfurous (due to the breakdown of sulfur - containing amino acids).
# Answer:
An example is milk spoilage. Fresh milk has a mild odor, but when it spoils (a chemical change), it develops a sour odor due to the production of lactic acid and other compounds from bacterial or enzymatic action. (Or: Cooking eggs - raw eggs have one odor, and when cooked (chemical change, protein denaturation), the odor changes, sometimes becoming slightly sulfurous.)

### Question 13
# Brief Explanations:
Some physical changes are reversible, like melting ice (liquid water can be frozen back to ice), but some are not. For example, tearing a piece of paper is a physical change, and you can't put the torn pieces back to form the original paper. So a physical change is sometimes reversible.
# Answer:
ST (Sometimes True)

### Question 14
# Brief Explanations:
By definition, a chemical reaction is a process in which one or more substances (reactants) are converted into one or more different substances (products). So in every chemical reaction, reactants are changed into products.
# Answer:
AT (Always True)

### Question 15
# Brief Explanations:
According to the law of conservation of mass, the total amount of matter (mass) remains constant during a chemical reaction. However, in some cases, like when a gas is produced and escapes (e.g., baking soda reacting with vinegar to produce $\ce{CO_2}$ gas that escapes), the amount of matter present in the visible system (the beaker with the liquid, for example) appears to change. But in reality, the total mass (including the escaped gas) remains the same. So the amount of matter present appears to change sometimes.
# Answer:
ST (Sometimes True)

### Question 16
# Brief Explanations:
The law of conservation of mass states that matter cannot be created or destroyed in a chemical reaction. The total mass of reactants is equal to the total mass of products. So matter can never be created during a chemical reaction.
# Answer:
NT (Never True)

### Question 17
# Brief Explanations:
In a chemical reaction, the substances that react are called reactants, and the substances that are formed are called products. So the statement "The substances formed in a chemical reaction are called reactants" is never true.
# Answer:
NT (Never True)

Sovi.AI - AI Math Tutor

QUESTION IMAGE

Question

Explanation:

Question 11

Answer:

Question 12