Conservation of Mass

• Law of conservation of mass

  • In a chemical reaction mass is conserved , as no atoms are lost or made 
  • So the mass of the products is equal to the mass of the reactants
• Why must chemical symbol equations always be balanced

  • Chemical symbol equations must always be balanced to show that no atoms are lost or made (So mass is conserved) 
  • In other words, there must be the same number of atoms of each element on both sides of the equation
• An example of a chemical reaction that has a balanced chemical symbol equation is the reaction between solid iron and copper sulfate solution

  • When solid iron reacts with copper sulfate solution , a reaction takes place 
  • This produces solid copper and iron sulfate solution

  
• Calculate the mass of magnesium chloride produced (Remember - the mass of the products = the mass of the reactants)?

  95g of magnesium chloride

  
• Calculate the mass of sodium oxide produced?

  124g of sodium oxide produced

  
• Calculate the mass of calcium carbonate that reacted?

  200g of calcium carbonate

  
• Calculate the mass of magnesium oxide in the reaction?

  40g of magnesium oxide

  
• A half equation can be used to show what happens in a chemical reaction
• Losing Electrons in Half Equation - Guide

  
• Gaining Electrons in Half Equation - Guide

  
• The balanced symbol equation for the reaction between iron and copper sulfate can be split into 2 half equations:

  • The iron atoms lose two electrons to form Fe²⁺ ions 
  • Fe (s) → Fe²⁺ (aq) + 2e⁻ 
  • The Cu²⁺ ions gain two electrons to form copper atoms 
  • Cu²⁺ (aq) + 2e⁻ → Cu (s)