C7 - Energy changes

• What is the principle of energy conservation in chemical reactions?

  Energy is neither created nor destroyed
• What is an exothermic reaction?

  Energy is transferred to surroundings
• What is an endothermic reaction?

  Energy is transferred to reactants
• What is the purpose of instant cold packs?

  Minimize damage after an injury
• How are exothermic changes utilized in everyday products?

  • Used in hand warmers
  • Used in self-heating cans
  • Crystallisation in reusable warmers
  • Disposable warmers heat surroundings longer
• What is the difference between bond breaking and bond making in terms of energy?

  • Bond breaking is endothermic
  • Bond making is exothermic
• What energy must be supplied in chemical reactions?

  Energy to break bonds between atoms
• What happens when new bonds are formed in a chemical reaction?

  Energy is released
• In an exothermic reaction, what is true about energy changes?

  More energy is released than absorbed
• In an endothermic reaction, what is true about energy changes?

  Less energy is released than absorbed
• How can you calculate the overall energy change in a chemical reaction?

  Using bond energies
• What do metals tend to do in chemical reactions?

  Lose electrons and form positive ions
• What occurs when two metals are dipped in a salt solution and joined by a wire?

  The more reactive metal donates electrons
• What is produced by the electrical cell formed by two metals?

  A voltage based on reactivity difference
• What is a major drawback of fossil fuels?

  They are non-renewable and cause pollution
• How can hydrogen be used as an alternative fuel?

  Burned in engines or used in fuel cells
• What is the waste product of hydrogen fuel cells?

  Water
• What role does hydrogen gas play in fuel cells?

  It provides a source of electrons