Rates of Reactions: Physical and Chemical Changes
This page introduces the fundamental concepts of rates of reactions in National 5 Chemistry. It distinguishes between physical and chemical changes and explores the energy dynamics of reactions.
Physical changes are characterized by no new substance formation and are generally easy to reverse. An example provided is ice melting.
Example: Ice melting is a physical change as it doesn't create a new substance and can be easily reversed by freezing.
Chemical reactions, on the other hand, result in the formation of new substances and are typically difficult to reverse. Combustion is given as an example of a chemical reaction.
Highlight: Understanding the difference between physical and chemical changes is crucial for analyzing reaction processes.
The page also introduces endothermic and exothermic reactions:
Definition: Endothermic reactions absorb energy from the surroundings, resulting in a decrease in temperature. Ice packs are an example of this process.
Definition: Exothermic reactions release energy to the surroundings, often resulting in an increase in temperature. Combustion is a common exothermic reaction.
Indicators of chemical reactions are listed, including color change, precipitate formation, temperature change, light production, and effervescence (bubble production).
The page then delves into factors affecting rate of reaction in N5 chemistry. These factors include:
- Concentration: Higher concentration leads to faster reaction rates due to increased chances of molecular collisions.
- Catalysts: Their presence increases reaction rates by reducing the energy required for the reaction to occur.
- Particle size: Larger particles decrease reaction rates due to reduced surface area for reactions.
- Temperature: Increasing temperature speeds up reactions by making molecules move faster, increasing collision chances.
Vocabulary: Effervescence refers to the production of bubbles in a chemical reaction.
