Glossary
Activation Energy
The minimum amount of kinetic energy that colliding reactant particles must possess for a reaction to occur.
Example:
Even if molecules collide, if they don't have enough energy to overcome the activation energy, they will just bounce off each other without reacting.
Average Kinetic Energy
The mean energy of motion of the particles in a system, directly proportional to the absolute temperature.
Example:
At room temperature, gas molecules have a certain average kinetic energy, which increases if the gas is heated.
Catalyst
A substance that increases the rate of a chemical reaction without being consumed in the process, typically by lowering the activation energy.
Example:
Enzymes in your body act as biological catalysts, speeding up vital reactions like digestion without being used up themselves.
Cold Object
An object possessing a lower temperature relative to its surroundings or another object.
Example:
An ice pack is a cold object used to reduce swelling by absorbing heat from an injured area.
Collision Rate
The frequency at which reactant molecules collide with each other in a given volume.
Example:
Increasing the pressure of a gas reaction increases the collision rate because the molecules are closer together.
Collision Theory
A model that explains how chemical reactions occur at the molecular level, stating that reactant particles must collide with sufficient energy and proper orientation.
Example:
The Collision Theory helps explain why increasing the concentration of reactants speeds up a reaction – there are simply more opportunities for effective collisions.
Heat Transfer
The movement of thermal energy from a region of higher temperature to a region of lower temperature.
Example:
When you place an ice cube in a warm drink, heat transfer occurs from the drink to the ice, causing the ice to melt.
Hot Object
An object possessing a higher temperature relative to its surroundings or another object.
Example:
A freshly baked cookie is a hot object that will transfer heat to your hand.
Proper Orientation
The specific alignment of reactant molecules during a collision that allows for the breaking of old bonds and the formation of new ones.
Example:
For a reaction between two complex molecules, they must collide at the correct active sites, demonstrating the importance of proper orientation.
Successful Collision
A collision between reactant molecules that results in the formation of products, requiring both sufficient energy and proper orientation.
Example:
Only a small fraction of all collisions are successful collisions because most lack the necessary energy or alignment.
Temperature
A measure of the average kinetic energy of the particles within a substance.
Example:
When you boil water, the temperature increases, indicating that the water molecules are moving faster on average.
Thermal Equilibrium
A state where two or more objects in contact have reached the same temperature, resulting in no net flow of heat between them.
Example:
After leaving a hot cup of coffee on the counter for a while, it will eventually reach thermal equilibrium with the room.
Zeroth Law of Thermodynamics
A fundamental law stating that if two systems are each in thermal equilibrium with a third system, then they are in thermal equilibrium with each other.
Example:
If a thermometer (system A) reads the same temperature for a cup of water (system B) and a block of metal (system C), then the Zeroth Law of Thermodynamics tells us the water and metal are also at the same temperature.