NGS Ch 10 - Section 3: Chemical Reactions

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Chemical Reaction

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Substances converted into new substances

Answer explanation

A chemical reaction is defined as a process where substances are converted into new substances, which distinguishes it from mere mixing or physical changes like freezing or heating without alteration.

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New substances in a chemical reaction

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Products

Answer explanation

In a chemical reaction, the new substances formed are called products. Reactants are the starting materials, while compounds and elements refer to specific types of substances, not the result of a reaction.

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Example of a chemical reaction

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Lighting a match

Answer explanation

Lighting a match is a chemical reaction because it involves a combustion process, producing heat and light, and resulting in new substances. In contrast, breaking glass, boiling water, and melting ice are physical changes.

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Chemical reaction description

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Chemical formulas and symbols

Answer explanation

A chemical equation uses chemical formulas and symbols to represent the substances involved in a reaction and their changes. This allows for a clear and concise depiction of the reaction, unlike words or pictures.

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Substances that react in a chemical reaction

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Reactants

Answer explanation

In a chemical reaction, the substances that undergo change are called reactants. They are transformed into products as a result of the reaction.

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Coefficient in a chemical equation

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Number of units of each substance

Answer explanation

The coefficient in a chemical equation indicates the number of units of each substance involved in the reaction. This helps balance the equation and shows the relative amounts of reactants and products.

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Subscript in chemical formula

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Number of atoms in a molecule

Answer explanation

The subscript in a chemical formula indicates the number of atoms of each element in a molecule. For example, in H2O, the '2' indicates there are two hydrogen atoms, making 'The number of atoms in a molecule' the correct choice.

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Law of Conservation of Mass

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Total starting mass = total final mass

Answer explanation

The law of conservation of mass states that in a closed system, the total mass remains constant. Therefore, the correct answer is that total starting mass equals total final mass, meaning mass cannot be created or destroyed.

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Atoms during a chemical reaction

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Shuffled around

Answer explanation

During a chemical reaction, atoms are not created or destroyed; instead, they are rearranged or shuffled around to form new substances. This is a fundamental principle of chemical reactions.

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NOT part of a chemical equation

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Temperatures

Answer explanation

In a chemical equation, the main components are reactants, products, and coefficients. Temperatures are not part of the equation itself, but may be noted separately, making 'Temperatures' the correct answer as it is NOT a part of a chemical equation.