Question

use words from the word - bank to complete the sentences. word bank: density, boiling point, solution, 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 because it helps us balance chemical equations and understand the quantitative relationships in chemical reactions.
3. A physical change is a change in the physical properties of a substance (such as state, shape, or size) without changing its chemical composition (e.g., melting ice). A chemical change results in the formation of new substances with different chemical properties (e.g., burning wood).
4. Coefficients in a chemical equation represent the relative number of moles of each reactant and product, and they are used to balance the equation according to 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.

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 is important for balancing chemical equations and understanding quantitative relationships in reactions.
3. Physical change: change in physical properties without changing chemical composition (e.g., melting ice). Chemical change: formation of new substances with different chemical properties (e.g., burning wood).
4. Coefficients represent relative number of moles of reactants and products and are used to balance chemical equations.
5. Open - system: matter and energy can be exchanged with surroundings. Closed - system: only energy can be exchanged, matter cannot.