Question

use words from the word - bank to complete the sentences. word bank: density, boiling point, solvent, reactant, chemical change, solubility, subscript, catalyst, toxicity, exothermic reaction. a _ shows how many atoms of an element are in a compound. a _ involves the formation of new substances. a _ is a combination of a solute and a solvent. a substance with high _ can be harmful in small amounts. the _ is the temperature at which a substance becomes a gas. a _ is a substance that helps speed up a chemical reaction. in a reaction, the substance that starts the process is the _. the _ of a substance is how much of it can dissolve in a solvent. an _ releases heat and feels warm. _ measures the mass per unit volume of a substance. write in your answers to the following questions: 1. what is the law of conservation of mass, and why is it important in chemical reactions? 2. describe the difference between a physical change and a chemical change. provide one example of each. 3. what is the role of coefficients in a chemical equation? 4. explain the difference between an open - system and a closed system during a reaction.

Explanation:

1. A subscript shows how many atoms of an element are in a compound. A chemical change involves the formation of new substances. A solution is a combination of a solute and a solvent. A substance with high toxicity can be harmful in small amounts. The boiling - point is the temperature at which a substance becomes a gas. A catalyst is a substance that helps speed up a chemical reaction. In a reaction, the substance that starts the process is the reactant. The solubility of a substance is how much of it can dissolve in a solvent. An exothermic reaction releases heat and feels warm. Density measures the mass per unit volume of a substance.
2. The Law of Conservation of Mass states that in a chemical reaction, the total mass of the reactants is equal to the total mass of the products. It is important in chemical reactions as it helps in balancing chemical equations and understanding the quantitative relationships between substances involved in a reaction.
3. A physical change is a change in which the substance's physical appearance changes but its chemical composition remains the same, e.g., melting of ice. A chemical change is a change in which new substances with different chemical properties are formed, e.g., rusting of iron.
4. Coefficients in a chemical equation represent the relative number of moles of each substance involved in the reaction. They are used to balance the equation to satisfy the Law of Conservation of Mass.
5. In an open - system, matter and energy can be exchanged with the surroundings. In a closed - system, only energy can be exchanged with the surroundings, while matter cannot enter or leave the system.

Answer:

1. Subscript; Chemical change; Solution; Toxicity; Boiling point; Catalyst; Reactant; Solubility; Exothermic reaction; Density
2. The Law of Conservation of Mass states that in a chemical reaction, the total mass of the reactants equals the total mass of the products. It's important for balancing equations and understanding quantitative relationships.
3. Physical change: change in physical appearance, same chemical composition (e.g., melting ice). Chemical change: new substances formed (e.g., rusting iron).
4. Coefficients represent relative number of moles and are used to balance equations for mass - conservation.
5. Open - system: matter and energy exchange with surroundings. Closed - system: only energy exchange, no matter exchange.