Presentation on theme: "Unit 1 ENERGY 1.1 How do you read a heating and cooling curve? March 22, 2010 Objective: SWBAT identify the parts of a heating curve and a cooling curve."— Presentation transcript:
Unit 1 ENERGY 1.1 How do you read a heating and cooling curve? March 22, 2010 Objective: SWBAT identify the parts of a heating curve and a cooling curve DO NOW: Heat of Reaction (ΔH) = H Products - H Reactants (ΔH) = D - A
Lets think of something heating up… 1.What happens to its temperature? 2. What happens to particles of the substance? It increases because HEAT IS ADDED Particles start to spread out
Lets study the graph 1. What phase changes do you notice on the graph? Solid turning to liquid Melting Liquid turning to gas Boiling
MELTING This is also known as fusion. During the melting process, the temperature remains constant even though heat is still being added at a constant rate. Both solid and liquid phases of the substance are present during the melting process. As time goes on, the amount of liquid continually increases and the amount of solid continually decreases. The amount of heat needed to convert a solid at its melting point to a liquid is called the heat of fusion.
And then… When the entire solid has melted and only the liquid phase is present, the temperature once again begins to rise. The temperature continues to rise until the boiling point is reached.
BOILING This is also known as vaporization. Once boiling begins, the temperature remains constant as the energy increases. During this phase change, both the liquid and gaseous (vapor) phases are present. The amount of heat needed to convert a liquid at its boiling point to a gas is called the heat of vaporization.
COOLING CURVE Task: After learning how a heating curve works, construct a cooling curve with a partner. Label the parts: Freezing Condensing
Lets Review What is reverse of boiling? What is reverse of melting? condensation freezing Also known as SOLIDIFICATION
SUBLIMATION AND DEPOSITION Some substances change directly from a solid to a gas without passing through a liquid phase. The process, in which a solid changes directly into a gas, is called sublimation. The reverse of sublimation, in which a gas changes directly into a solid, is called deposition.
Lets Try Some 1. The temperature of a sample of a substance is increased from 20.°C to 160.°C as the sample absorbs heat at a constant rate of 15 kilojoules per minute at standard pressure. The graph below represents the relationship between temperature and time as the sample is heated.
a)What is the boiling point of this sample? b) What is the total time this sample is in the liquid phase, only? c) What is the melting point of this sample? d) What is the range of temperature at which the sample is in the gas phase, only? Between 4 minutes and 7 minutes = 3 minutes 120 o C 70 o C 120 o C- 160 o C
2. The graph below shows a compound being cooled at a constant rate starting in the liquid phase at 75°C and ending at 15°C.
a) What is the freezing point of the compound, in degrees Celsius? b) State what is happening to the average kinetic energy of the particles of the sample between minute 2 and minute 6. c) A different experiment was conducted with another sample of the same compound starting in the solid phase. The sample was heated at a constant rate from 15°C to 75°C. Draw the resulting heating curve. d) What Kelvin temperature is equal to 15°C? 50 o C ( Kinetic=motion) since temperature decreases, Kinetic energy also decreases
273K = 0 o C So 15 o C = ?K = 288K
INDEPENENT PRACTICE COMPLETE FOR HOMEWORK IF YOU ARE NOT DONE IN CLASS. ASSIGNMENT IS TO BE COMPLETED BY TOMORROW!!!