Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Matter is composed of tiny particles that are in constant motion. In a solid, these particles are held together by strong inter-particle forces of attraction.
The melting point is the temperature at which a solid starts changing into a liquid at atmospheric pressure. At this point, the kinetic energy of particles is sufficient to overcome the forces of attraction. For ice, this is or .
During the change of state from solid to liquid, the temperature remains constant until the entire substance has melted. The heat energy supplied is used to change the state by breaking the bonds between particles, rather than increasing the temperature.
Latent Heat of Fusion is the amount of heat energy required to change of a solid into a liquid at its melting point at atmospheric pressure. It is called 'latent' or hidden because it does not show a rise in temperature on the thermometer.
Particles in water at () have more energy than particles in ice at the same temperature because the water particles have absorbed the Latent Heat of Fusion.
📐Formulae
💡Examples
Problem 1:
Convert a temperature of to the Celsius scale.
Solution:
Explanation:
To convert from Kelvin to Celsius, we subtract (or simply for Grade 8 level calculations) from the Kelvin temperature value.
Problem 2:
Why is the temperature of melting ice constant at even though we continue to heat it?
Solution:
The heat is absorbed as Latent Heat of Fusion.
Explanation:
When ice reaches , the heat energy being supplied is used to overcome the intermolecular forces of attraction between the molecules to convert them from a solid lattice to a liquid state. Since this energy is consumed in the change of state, the kinetic energy of the particles does not increase, and thus the temperature remains constant.
Problem 3:
Calculate the temperature in Kelvin for the boiling point of water, which is .
Solution:
Explanation:
Using the formula , we add to the Celsius value of the boiling point.