Chemical and Physical Changes Quiz

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Questions and Answers

What distinguishes a chemical change from a physical change?

  • Chemical changes are reversible.
  • Chemical changes involve breaking or forming bonds. (correct)
  • Physical changes create new substances.
  • Physical changes result in a color change.

Which of the following is a physical change?

  • Burning wood.
  • Mixing vinegar and baking soda.
  • Rust forming on iron.
  • Dissolving sugar in water. (correct)

Which of the following indicators is most likely to signify a chemical change?

  • The color of the substance stays the same.
  • The substance remains unchanged.
  • A solid forms from mixing two liquids. (correct)
  • The substance becomes colder.

What is the correct name for the compound formed when sodium and chlorine react?

<p>Sodium Chloride (A)</p> Signup and view all the answers

What do the reactants represent in a chemical reaction?

<p>Substances present at the beginning of the reaction. (B)</p> Signup and view all the answers

How should the state of matter be indicated in a chemical equation?

<p>By adding the state symbols next to each reactant and product. (C)</p> Signup and view all the answers

Which of the following is true regarding the conservation of mass in a chemical reaction?

<p>Mass remains constant throughout the reaction. (B)</p> Signup and view all the answers

What is a word equation?

<p>A description of a chemical reaction using only names of reactants and products. (C)</p> Signup and view all the answers

What does the conservation of mass state about reactants and products in a chemical reaction?

<p>The total mass of the reactants is equal to the total mass of the products. (D)</p> Signup and view all the answers

Which of the following scenarios would violate the principle of conservation of mass?

<p>A gas escapes from an open container during a reaction. (A)</p> Signup and view all the answers

What role do coefficients play in balancing a chemical equation?

<p>They represent the number of molecules of each reactant and product. (C)</p> Signup and view all the answers

In the reaction C + Cl2 → CCl4, how can you balance the equation correctly?

<p>By adding a coefficient of 2 to Cl2. (C)</p> Signup and view all the answers

Why can subscripts not be altered when balancing chemical equations?

<p>Changing subscripts alters the identity of the compounds involved. (C)</p> Signup and view all the answers

If 2.5g of Copper reacts with 3g of oxygen and produces 5.5g of copper sulfide, what can you infer?

<p>Mass is conserved during the reaction. (A)</p> Signup and view all the answers

What happens when experiments require materials to be dissolved or evaporated?

<p>They can potentially result in apparent mass loss. (D)</p> Signup and view all the answers

Which statement describes the concept of balancing a chemical equation?

<p>It involves changing the coefficients to equalize the number of atoms. (C)</p> Signup and view all the answers

Flashcards

Physical Change

A change in the appearance of a substance, but not its chemical composition. No new substances are formed, and chemical bonds are not broken or formed.

Chemical Change

A change where new substances are formed, and chemical bonds are broken and formed. This change is usually irreversible.

Reactants

The chemicals that exist before a chemical reaction takes place. They are the ingredients.

Products

The new chemicals that are formed after a chemical reaction. They are the result of the reaction.

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Word Equation

A written representation of a chemical reaction using the names of the substances involved. It doesn't use chemical symbols or formulas.

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State Symbols

Symbols used in chemical equations to indicate the state of matter of each reactant and product: (s) for solid, (l) for liquid, (g) for gas, and (aq) for aqueous solution.

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Conservation of Mass

The principle that states that the total mass of the reactants in a chemical reaction is equal to the total mass of the products. No mass is lost or gained during a chemical reaction.

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Rules for Naming Compounds

A rule used for naming compounds based on the number of elements involved and whether oxygen is present. It dictates the ending of the compound's name.

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Balancing Chemical Equations

Balancing chemical equations ensures that the number of atoms of each element on the reactants' side equals the number on the products' side. This adheres to the law of conservation of mass.

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Coefficients

The numbers written in front of chemical formulas in an equation to indicate the relative number of molecules or atoms involved in the reaction. They help balance the equation.

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Subscripts

The small numbers written as subscripts after an element symbol in a chemical formula. They indicate the number of atoms of that element in a molecule.

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Balanced Chemical Equation

A chemical equation is balanced when the number of atoms of each element on the reactants' side is equal to the number of atoms of that element on the products' side. It illustrates the law of conservation of mass.

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Unbalanced Chemical Equation

A chemical equation that doesn't have the same number of atoms of each element on both sides, violating the law of conservation of mass.

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Study Notes

Physical Changes

  • Physical changes alter appearance but do not form or break chemical bonds.
  • A new substance is not created.
  • Examples include melting ice, mixing salt and water, and crumpling paper.

Chemical Changes

  • Chemical changes create new substances by forming or breaking chemical bonds.
  • These changes are irreversible.
  • Indicators of chemical change: fire, temperature changes, explosions, odors, color changes, bubbling/fizzing.

Three Golden Rules of Chemical Reactions

  • Chemical reactions are typically irreversible.
  • They create new substances.
  • They involve an energy change.

Naming Compounds

  • Rule 1: When two elements combine (e.g., metal + non-metal), the ending is usually "-ide" (e.g., Sodium Chloride).
  • Rule 2: When three or more elements combine, if one is oxygen, the ending is "-ate" (e.g., Copper Sulphate).
  • The metal's name comes first, followed by the non-metal with the changed ending.

Metals and Non-metals with Oxygen

  • When metals combine with oxygen, the compound is named with the metal first, followed by the nonmetal ending changed to "-ate".
  • Example: Copper Sulphate

Reactants and Products

  • Reactants: The substances at the start of a reaction.
  • Products: The new substances formed during the reaction.
  • Atoms in reactants are rearranged to form products.

Word Equations

  • Word equations describe reactions using names of substances, not chemical formulas or symbols.
  • An example is: Copper + Oxygen → Copper Oxide.
  • The arrow indicates the direction of the reaction.

State Symbols

  • State symbols indicate the physical state of reactants and products.
  • Symbols:
    • Solid (s)
    • Liquid (l)
    • Gas (g)
    • Aqueous solution (aq)
  • Example: Hydrogen (g) + oxygen (g) → water (l)

Conservation of Mass

  • Mass remains constant in a chemical reaction: reactants' mass equals products' mass.
  • Atoms are rearranged, not created or destroyed.
  • Example: 2.5 g copper + 3 g oxygen → 5.5 g copper oxide

Balancing Chemical Equations

  • No atoms are created or destroyed during a chemical reaction.
  • Balancing involves adjusting coefficients (numbers in front of formulas) to make the number of each atom the same on both sides of the equation.
  • Subscripts (small numbers below elements) cannot be changed.
  • Example: C + 2Clâ‚‚ → CClâ‚„ (balanced)

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