Explosions: Chemical and Physical Reactions

• Explosions involve identifying the difference between chemical and physical reactions, explaining particle theory, and linking particle theory to gas pressure.

Key Words

• Explosion, physical reaction, chemical reaction, reactants, and pressure.

Spellings to learn

• Chemical, reaction, explosive, flammable, particle theory, physical change, rust, pressure, word equation, electrolysis, reactivity series, reducing agent, sacrificial protection, endothermic reaction, exothermic reaction, hydrocarbon, oxidising agent, displace, displacement, oxidation, mineral, and reduced.

Entrance Activity

• Explosions cause a sudden release of pressure, gas, heat, and light when subjected to shock, pressure, or high temperature.
• Examples of explosions are volcanic eruptions, geysers, fireworks, and atomic bombs.

Physical Change

• The Mentos and Coke reaction is an example of physical change, where no new substance is made.
• The explosion results from a sudden increase in volume in the form of gas and a transfer of energy to the surroundings.
• Natural explosions such as geysers and volcanoes, can also be caused by physical changes.

Key Definitions

• Chemical Change: New substances are made, and chemical reactions typically have a change in appearance and energy.
• Physical Change: No new substances are made, but there is a change in the appearance of a chemical, involving a state change or dissolving.

Chemical Change

• Atoms are rearranged to form new products with different properties.
• Hydrogen and oxygen combine to form water.
• Mass is always conserved, never lost or gained, in chemical reactions.

Particle Theory

• Matter is composed of tiny particles that are always in motion.
• Forces of attraction hold particles together, varying in strength depending on the state of matter.
• Particles possess different amounts of energy and react differently under pressure.

Particle Theory and Pressure

• The forces of particles hitting container walls cause pressure in gases.

Increasing Pressure

• Pressure can be increased by
  • Increasing the number of particles.
  • Reducing the size of the container.
  • Increasing the temperature.
• Pressure increases due to the number of collisions with the sides of a container.

Example Explosion

• A plastic bottle of liquid nitrogen quickly turns into gas and increases pressure until the bottle gives way, causing an explosion.
• Explosions cause a sudden increase in volume with a transfer of energy to the surroundings.
• This is an example of physical change, while volcanoes and geysers can also be natural physical explosions.

Changes and Pressure Questions

• Condensation is a physical change, while neutralization is a chemical reaction.
• Chemical reactions form new substances, but physical changes can usually be reversed easily.
• With a burning candle, the pool of liquid signifies a physical change, while the yellow flame indicates a chemical reaction.
• A gas exerts pressure due to the force of particles hitting the walls of the container.
• Gas pressure increases as the temperature increases, and decreases as the number of gas particles decreases.
• Gas pressure does not increase as the volume of the container increases, and is false.