Energy Changes

Energy Changes

• Energy changes can occur through various processes, often involving the transfer of heat.

• Examples include:

  • Hand Warmers: Activation by shaking leads to a release of heat energy, warming hands.

  • Candles: Burning produces heat that warms the surrounding air.

  • Incandescent Light Bulbs: The flow of electrons through the filament generates both light and heat.

Thermochemistry

• Definition: The study of energy changes during:

  • Chemical Reactions: Energy is absorbed or released when bonds are broken / formed.

  • Changes of State: Energy changes when matter transitions between solid, liquid, and gas states.

• Energy Characteristics:

  • Energy provides the capacity for doing work or supplying heat.

  • It has no mass or volume and is detected by its effects.

Chemical Potential Energy

• Energy stored in the chemical bonds of substances (covalent and ionic bonds).

  • Energy is released when bonds are broken.

  • Example: Gasoline - stored energy is released during combustion, producing heat and work.

Types of Fuels and Emissions

• Petrol vs. Diesel: Both fuels have different combustion characteristics, affecting emission output.

  • Petrol: Highly volatile, burns readily.

  • Diesel: Longer molecules, harder to ignite, resulting in less volatile emissions.

Heat Transfer (q)

• Heat (q): Represents energy transfer due to temperature difference.

  • Transfers spontaneously from warmer to cooler objects.

  • Example: When in cold weather without a coat, your body releases heat to the cooler environment.

Ice Water Example

• Heat flows from warmer water to ice, causing the ice to melt as heat is absorbed.

  • Temperature flow: Warm water melts the solid ice, causing heat to leave the water.

Chemical Reactions and Energy Changes

• Energy released during combustion stored in hydrocarbons.

• Example: Burning wood releases energy stored in its chemical bonds.

System and Surroundings

• System: The part of the universe focused on; everything else is surroundings.

• Law of Conservation of Energy: Energy cannot be created or destroyed; it can only change forms.

  • If the system's energy increases, the surroundings' energy decreases.

Endothermic vs. Exothermic Processes

• Endothermic: Heat flows into a system from its surroundings; defined with a positive q value.

  • Example: Ammonium nitrate dissolving in water absorbs heat, causing temperature to decrease.

• Exothermic: Heat released from a system to its surroundings; defined with a negative q value.

  • Example: Combustion reactions release heat into the environment.

Real-World Examples

• Endothermic Process: Person near a fireplace absorbs heat from the heat source.

• Exothermic Process: A sweaty athlete releases heat to the environment as they cool off.

Snow Melting Scenario

• Melting snow on rooftops that refreezes into icicles represents heat flow direction.

• As water freezes, heat leaves the water and enters the air, making it an exothermic process.