37. The Reactivity Series: Metal Reactions & Displacement

The Reactivity Series: Metal Reactions & Displacement

Based on the video, here are the notes on the reactivity series, how metals react with acids and water, and the principles of displacement reactions.

1. Defining Reactivity

Reactivity is a measure of how easily a metal atom loses its outer shell electrons to form a positive ion.

• Most Reactive: Metals that lose electrons very easily (e.g., Group 1 metals like Potassium and Sodium).

• Least Reactive: Metals that do not form ions easily (e.g., Transition metals like Copper and Gold).

• Reference Elements: Although they are not metals, Carbon and Hydrogen are often included in the series as reference points for comparison.

2. Reactions with Acids

When a metal reacts with an acid, it produces a salt and hydrogen gas.

• Observations:

  • Potassium/Sodium: React explosively, producing significant heat and catching fire.

  • Magnesium: Reacts vigorously with lots of bubbles (fizzing).

  • Zinc/Iron: React more slowly with fewer bubbles.

  • Copper: Does not react with dilute acids at all.

• Measuring Reactivity: To compare reactivity scientifically, you can measure the temperature change (the more reactive the metal, the more heat is produced). To ensure a fair test, keep the mass, surface area, and acid concentration constant.

3. Reactions with Water

Only the most reactive metals react significantly with cold water to form a metal hydroxide and hydrogen.

• Potassium, Sodium, Lithium: React vigorously with water.

• Magnesium: Reacts very slowly with cold water (but faster with steam).

• Zinc, Iron, Copper: Do not react with cold water at all.

4. Displacement Reactions

A displacement reaction occurs when a more reactive metal takes the place of a less reactive metal in a compound.

• Rule: A metal can only displace a metal that is lower than it in the reactivity series.

• Examples:

  • Magnesium + Iron Sulfate → Magnesium Sulfate + Iron (Possible because Magnesium is more reactive than Iron).

  • Copper + Iron Sulfate → No Reaction (Not possible because Copper is less reactive than Iron).

5. Summary Table (General Order)