Chemical Reactions and Changes Quiz

Chemical Reactions

• A chemical reaction is the interaction of substances to create new substances.
• Reactants are the substances that react (on the left of the arrow).
• Products are the substances that are made (on the right of the arrow).
  • Example: A + B → C + D (A and B react to form C and D).

Chemical Change vs Physical Change

• Chemical change occurs when a chemical reaction creates new substances.
• Physical change occurs when no new substances are made.
  • Example: Rusting iron (chemical change) vs. water molecules maintaining the same structure (physical change).

Compound Formulae 1

• Compound formulae use symbols and small numbers to represent the elements and atoms in a compound.
• The small number(s) after an element symbol shows how many atoms of that element are present in the compound.
• Capital letters represent elements, and lower case letters (if any) are part of the element symbol.
• Example: Water (H₂O) has 2 hydrogen atoms, and 1 oxygen atom.

Compound Formulae 2

• "Big numbers" at the start of a chemical formula indicate the number of molecules.
• Example: 2H₂O represents 2 molecules of water, having 4 hydrogen atoms and 2 oxygen atoms.

Writing Formulae From a Structure

• Chemical formulae can be derived from a diagram of a chemical structure.
• Count the number of each type of atom.
• Example: Ethane (C₂H₆) - 2 carbon atoms and 6 hydrogen atoms.

Compound Formulae With Brackets 1

• Brackets in chemical formulae indicate a group of atoms that act as a single unit.
• The number outside the bracket multiplies everything inside the bracket.
• Example: Magnesium hydroxide (Mg(OH)₂) - 1 magnesium atom, 2 oxygen atoms, and 2 hydrogen atoms.

Compound Formulae With Brackets 2

• "Big numbers" at the start of a chemical formula represent the number of molecules containing the grouped atoms.
• Example: 2Mg(OH)₂ has 2 magnesium atoms, 4 oxygen atoms, and 4 hydrogen atoms in total.

Compound Formulae Examples

• Chemical formulae can depict the atoms within compounds.
• Example: Mg(NO₃)₂ has 1 magnesium atom, 2 nitrogen atoms, and 6 oxygen atoms.
• Example: 3Mg(NO₃)₂ has 3 magnesium atoms, 6 nitrogen atoms, and 18 oxygen atoms.

Relative Formula Mass (No Brackets)

• The relative formula mass (Mr) of a compound shows the total atomic mass of all atoms in the compound.
• Calculated by adding the relative atomic mass of atoms in a compound.
• Example: H₂O - (2 × 1) + (1 × 16) = 18

Relative Formula Mass (With Brackets)

• Example: Mg(NO₃)₂ - Mr = (1 × 24) + (2 × 14) + (6 × 16) = 148

Scatter Graphs

• Scatter graphs show the relationship between two variables.
• The independent variable is on the x-axis, and the dependent variable is on the y-axis.
• Data points are plotted, and a line of best fit can be drawn.

Naming Compounds (Words)

• The names of elements change when bonded in compounds.
• Group 7 elements become -ide (e.g., chloride).
• Group 6 elements become -ide (e.g., oxide).
• In more complex compounds, naming parts of the compound names changes depending on the other elements (e.g, sulfate, carbonate).

Naming Compounds (Chemical Formulae)

• Chemical formulae can be used to name compounds.
• Example: NaF - sodium fluoride
• Example: Li₂S - lithium sulfide

Chemical Word Equations

• Word equations use the names of reactants and products in a reaction.
• Example: Carbon + Oxygen → Carbon dioxide

Chemical Symbol Equations

• Chemical symbol equations use chemical symbols to represent reactants and products.
• Example: C + O₂ → CO₂