chemical reactions

• What is an element made of?

  Atoms with the same number of protons
• How do non-metallic elements in Group 0 exist?

  As individual atoms
• What is the formula for non-metallic elements in Group 0?

  It is the same as their symbol
• What do many non-metallic elements exist as?

  Molecules and giant structures
• What happens in chemical reactions involving elements?

  New substances are made
• How do atoms combine in chemical reactions?

  In fixed ratios for full outer shells
• What is a compound?

  A pure substance of chemically combined elements
• How can compounds be separated?

  They cannot be separated by physical means
• How do the properties of compounds compare to their elements?

  They are usually quite different
• What does a chemical formula indicate?

  The ratio of atoms in a compound
• What do ionic compounds consist of?

  Metal and non-metal elements as ions
• How is the symbol of the metal element written in an ionic compound?

  Always written first
• What do sodium and chlorine form when they react?

  Sodium chloride (NaCl)
• What type of formula does an ionic compound have?

  Always an empirical formula
• Why is the formula of ionic compounds an empirical formula?

  It represents the simplest ratio of ions
• What is the SI unit of amount of substance?

  Mole (mol)
• What does one mole of a substance contain?

  The same number of particles as any substance
• What is the Avogadro number?

  6.02 x 10²³ mol^-1
• Why is the unit mol^-1 used?

  It indicates entities per mole of substance
• What is the mass of 1 mole of an element called?

  Molar mass
• How is the molar mass of an element expressed?

  Same as its relative atomic mass in grams
• How is the molar mass of a compound expressed?

  Same as its relative formula mass in grams
• How do you calculate the mass of one atom of an element?

  Divide molar mass by Avogadro constant
• How do you calculate the mass of one molecule of a compound?

  Divide molar mass by Avogadro constant
• What does the Law of Conservation of Mass state?

  No matter is lost or gained in reactions
• What must be true for all chemical equations?

  They must be balanced
• What is conserved during a chemical reaction?

  The total mass of reactants and products
• What does stoichiometry refer to?

  The numbers in front of reactants and products
• What are the numbers in a balanced equation called?

  Coefficients or multipliers
• How do you find the coefficients in a balanced equation?

  Convert masses to moles using molar masses
• What do you do if the mole results yield uneven numbers?

  Multiply all numbers by the same factor
• What is the process of balancing a chemical equation?

  1. Identify reactants and products
  2. Write the unbalanced equation
  3. Adjust coefficients to balance atoms
  4. Ensure the same number of each atom on both sides
  5. Check that the equation is balanced
• What are the implications of the Law of Conservation of Mass in chemical reactions?

  • Mass is conserved in reactions
  • Total mass of reactants equals total mass of products
  • Changes of state do not affect mass conservation
  • Mass loss can occur if gases escape
• What are the characteristics of ionic compounds?

  • Composed of metal and non-metal ions
  • Formed through ionic bonds
  • Have empirical formulas
  • Exist as giant structures
• What are the differences between elements, compounds, and mixtures?

  • Elements: Pure substances made of one type of atom
  • Compounds: Pure substances made of two or more elements chemically combined
  • Mixtures: Combinations of two or more substances that retain their properties
• how to find the number of atoms from moles.

  • multiply the number of moles by avogadro's constant.
  • if the substance is a molecule [has a small number], you must multiply the answer by the small number.
• how to find the mass of one atom

  • divide the relative formula mass by avogadro's constant.
• how to work out limiting reactants

  • divide the mass of each substance by its Mr to calculate the number of moles.
  • divide by the number of the smallest number of moles.
  • compare the ratios between the moles of the products and the balanced equation.
  • the substance which has a higher ratio when calculated in masses vs. equation is in excess