Chapter 10 Energy
Energy What is energy? The potential to do work What is work? Change in self or surroundings Both work and energy are in units of joules (J) What are the forms of energy? Kinetic, Potential, Chemical, Electrical, Nuclear, Sound, Electrochemical, Thermal What is the formula for nuclear energy?
E = m c2
Energy calorie The law of conservation of energy Non-SI unit of energy 1 calorie of energy can raise the temperature of 1 gram of water by 1o C 1 calorie = 4.184 joules 1 cal = 4.184 J 1 Calorie = 1kcalories = 1000 calories The law of conservation of energy Energy cannot be created out of nothing, but it can be changed from one form to another Where does electrical energy come from?
Thermal Energy What is thermal energy? How is thermal energy measured? Internal kinetic energy How fast the particles are moving or vibrating How is thermal energy measured? thermometer
Heat Heat: transfer of thermal energy Thermal energy flows from high to low (high temperature objects transfer thermal energy to objects with lower temperature) Thermal energy is transferred by conduction, convection or radiation
Conduction: direct contact
Convection: requires a fluid (liquid or gas)
Radiation: via electromagnetic waves
Questions?
Change in thermal energy The amount of change in thermal energy can be estimated by determining the change in temperature. Change in Temp = final temp – initial temp ΔT = Tf – Ti also ΔT = T2 – T1
Check for understanding 1 calorie = _______ joules A typical 8.0 oz soda could have 110 Calories. That is equivalent to ________ joules. What is the change in temperature of a soda taken from a refrigerator (at 4o C) and consumed (normal body temp = 37o C)? In Antarctica, the temperature can drop from a high in the summer of 288 K to a low of 183 K in the winter. Calculate the temp change from summer to winter. 4.184 460000 37o C -105 K
Heat Capacity When energy is put into or taken away from an object, it can increase or decrease the object’s internal kinetic energy. Not all objects change temperature at the same rate as energy is added or taken away. Imagine going to a pool in the early morning and staying there through the afternoon.
Specific Heat Capacity The specific heat capacity is the amount of heat per unit mass required to raise the temperature by one degree Celsius. Specific heat can be measured in units of joules per gram oC (J/goC) The relationship between heat and temperature change is usually expressed in the form shown below where c is the specific heat, q is the heat required and ΔT is the change in temperature. q = m x C x ΔT
Heat Capacity How much energy is absorbed when 88.0 g of water is heated from 5.00o C to 37.0o C? q = m x C x ΔT C (of H2O) = 4.184 J/ g oC m = 88.0 g C = 4.184 J / g x C ΔT = 37o C - 5o C = 32o C) q = (88.0g)( 4.184J/go C)(32oC) q = 1.18 x 104 J or 11800 J
Enthalpy Enthalpy is a measure of the total energy of a thermodynamic system. What do you expect to see as you add energy to a substance?
Latent Heat Latent heat is the heat released or absorbed by a chemical substance during a change of state that occurs without a change in temperature a change of state, a phase transition such as the melting of ice or the boiling of water To calculate the energy required (either added or removed) for a phase change, use q = m ΔHfus or q = m x ΔHvap
Chapter 10 (in a nutshell) How is internal kinetic energy measured? Thermometer What units are used for temperature? Celsius, Kelvin, Fahrenheit the transfer of thermal energy is Heat What are the units for heat Joules What are the units for specific heat? J/goC
Chapter 10 (in a nutshell) What is a calorie? Unit of measure for energy & work The energy required to raise the temp of one gram of water by 1oC What device did we use in the lab to measure heat? Calorimeter How is specific heat calculated? Heat/(mass x temperature change)
Chapter 10 (in a nutshell) 1 cal = ____ joules 4.184 3 Cal = ____ joules 12552.