Chemical Reactions Overview

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Questions and Answers

What is the primary characteristic of a chemical reaction?

  • Only physical properties of substances change.
  • Atoms are rearranged to form new substances. (correct)
  • Energy is neither absorbed nor released.
  • Atoms are created or destroyed.

Which equation represents a correct balanced symbol equation?

  • Cu + O → CuO
  • 2Cu + O → CuO
  • 2Cu + Oâ‚‚ → 2CuO (correct)
  • Cu + 2O → 2CuO

In an exothermic reaction, energy is transferred to the surroundings which results in what change in temperature?

  • Temperature fluctuates randomly.
  • Temperature remains the same.
  • Temperature of the surroundings increases. (correct)
  • Temperature of the surroundings decreases.

What happens to mass during a chemical reaction according to the law of conservation of mass?

<p>Mass remains constant if closed systems are considered. (B)</p> Signup and view all the answers

What type of reaction involves a substance breaking down into simpler substances usually requiring heat?

<p>Thermal Decomposition (A)</p> Signup and view all the answers

Which fuel produces carbon dioxide and water when combusted?

<p>Natural gas (B)</p> Signup and view all the answers

Which term describes substances that speed up a reaction without being consumed in the process?

<p>Catalysts (D)</p> Signup and view all the answers

Which of the following is NOT a characteristic of a physical change?

<p>Chemical bonds are broken. (D)</p> Signup and view all the answers

What is the primary environmental concern associated with the combustion of fossil fuels?

<p>Contributing to climate change. (C)</p> Signup and view all the answers

Which of the following statements is true regarding combustion?

<p>Combustion reactions are a type of oxidation reaction. (D)</p> Signup and view all the answers

Flashcards

Chemical Reaction

A process that rearranges atoms to form new substances. Atoms are joined in different ways, resulting in changes to the substances involved.

Reactants

The substances that react in a chemical reaction.

Products

The substances produced by a chemical reaction.

Word Equation

A representation of a chemical reaction using words. It shows the reactants and products, separated by an arrow.

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Balanced Symbol Equation

A representation of a chemical reaction using chemical formulas. It shows the formulas of all substances involved and the relative number of atoms for each substance.

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Exothermic Reaction

A chemical reaction that releases energy to the surroundings, causing the temperature to increase.

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Endothermic Reaction

A chemical reaction that absorbs energy from the surroundings, causing the temperature to decrease.

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Conservation of Mass

A law stating that matter cannot be created or destroyed during a chemical reaction. The total mass of the reactants equals the total mass of the products.

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Catalyst

A substance that speeds up a chemical reaction without being used up in the process.

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Thermal Decomposition

A reaction where a complex substance breaks down into simpler substances, usually requiring heat.

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Study Notes

Chemical Reactions

  • A chemical reaction is the rearrangement of atoms to form new substances.
  • Reactants are the starting materials, products are the final substances.
  • Word equations use names of substances, symbol equations use formulas.
  • Example: Copper + Oxygen → Copper Oxide (word equation) ; 2Cu + Oâ‚‚ → 2CuO (symbol equation)

What Happens During a Reaction

  • All chemical reactions involve an energy transfer.
  • Endothermic Reactions: Energy is transferred from the surroundings to the reaction mixture. Reaction feels cold.
  • Exothermic Reactions: Energy is transferred from the reaction mixture to the surroundings. Reaction feels hot.
  • Examples of energy transfer: Thermal decomposition (heat needed for decomposition), Combustion (a fuel burning in oxygen).

Conservation of Mass

  • In a chemical reaction, atoms are neither created nor destroyed.
  • The total mass of the reactants equals the total mass of the products.
  • Mass can appear to change if there is a gas involved (it escapes).

Types of Reactions

  • Decomposition: A substance breaks down into simpler substances. Thermal decomposition specifically means it needs heating.
  • Combustion: A substance reacts with oxygen to release heat. An example is burning fuels.
  • Oxidation: A substance reacts with oxygen. Combustion is a type of oxidation reaction.

Speed of Reactions

  • Reactions can be fast or slow.
  • Catalysts speed up reactions without being used up.

Changes of State

  • Changes of state (solid, liquid, gas) are physical changes, not chemical reactions. They are reversible. For example: water, ice, and steam are all water (Hâ‚‚O) in different states.

Key Terms

  • Balanced symbol equation: An equation where the number of atoms of each element is the same on both sides of the equation.
  • Catalyst: A substance that speeds up a reaction without being used up.
  • Chemical reaction: A process that changes substances into new substances.
  • Combustion: A chemical reaction with oxygen which releases energy as heat and light.
  • Conservation of mass: The total mass of reactants equals the total mass of products.
  • Decomposition: A reaction where a complex substance breaks down into simpler substances.
  • Endothermic: A reaction that absorbs energy from the surroundings.
  • Exothermic: A reaction that releases energy to the surroundings.
  • Fossil fuel: A fuel formed from the remains of organisms over millions of years.
  • Fuel: A substance that reacts with oxygen to release energy.
  • Non-renewable: Resources that are used up faster than they are replaced.
  • Oxidation: A reaction between a substance and oxygen.
  • Physical change: A change in state or form of a substance without changing its chemical composition.
  • Product: The substance(s) formed in a chemical reaction.
  • Reactant: The substance(s) that react in a chemical reaction.
  • Renewable: Resources that can be replenished.

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