c7

• 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 absorbed from surroundings.
• What happens to energy in an exothermic reaction?

  It is released to the surroundings.
• What happens to energy in an endothermic reaction?

  It is absorbed from the surroundings.
• What would you feel when stirring potassium nitrate in water?

  The beaker feels cold to the touch.
• What can you deduce if the temperature of a reaction mixture increases from 19°C to 27°C?

  Energy is transferred from the mixture to surroundings.
• What is the energy required for the thermal decomposition of 16.8g of magnesium carbonate?

  23.4 kJ
• What is the balanced symbol equation for the thermal decomposition of magnesium carbonate?

  MgCO₃(s) → MgO(s) + CO₂(g)
• What endothermic change is used in cold packs?

  Dissolving ammonium nitrate.
• What is the formula of ammonium nitrate?

  NH₄NO₃
• What is another use of ammonium nitrate?

  Fertilizer in agriculture.
• What solid is used in self-heating coffee cans?

  Calcium chloride.
• Why must coffee stay out of contact with the solid in self-heating cans?

  To prevent unwanted reactions from occurring.
• What chemical reaction occurs in a disposable hand warmer?

  Oxidation of iron powder occurs.
• How does a reusable hand warmer work?

  By crystallization of sodium acetate solution.
• What are the advantages and disadvantages of disposable and reusable hand warmers?

  Advantages:

  • Disposable: Convenient and ready to use.
  • Reusable: Cost-effective over time.

  
  

  Disadvantages:

  • Disposable: Generates waste.
  • Reusable: Requires activation and preparation.
• Why is bond breaking considered an endothermic process?

  It requires energy to break bonds.
• What bonds are broken and formed in the reaction between methane and oxygen?

  Four C-H bonds broken, two O=O bonds formed.
• What is the process of bond breaking and making in chemical reactions?

  • Bonds are broken in reactants (endothermic).
  • New bonds are formed in products (exothermic).
  • Energy comparison determines reaction type.