some like it hot and some sweat when the heat is on!!!
Post on 23-Dec-2015
212 Views
Preview:
TRANSCRIPT
Thermodynamics and Specific Heat
Some Like it Hot and Some Sweat when the Heat is On!!!
https://www.youtube.com/watch?v=vqDbMEdLiCs
First Law of ThermodynamicsAll energy lost by one system must be
gained by the surroundings (another system)
System:A group of interacting objects and
effects that are selected for investigation.
Surroundings:Everything else except the system.
Types of SystemsOpen System
Matter and energy can be exchanged with the surroundings
Ex. An open coffee cup (w/o lid)
Types of SystemsClosed System:
Only energy is allowed to be exchanged with the surroundings
Ex. A coffee cup w/ lid
Types of SystemsIsolated System:Neither matter nor energy can be exchanged with surroundings
Ex. Insulated Thermos
Second Law of ThermodynamicsStates energy (heat)
spontaneously flows from higher temperature to lower temperature until it reaches thermal equilibrium.A condition where
the temperatures are the same and heat no longer flows
Hot Coffee
Heat Flow
Heat Flow
Specific HeatThe quantity of energy it takes per gram
of a certain material to raise the temperature by one degree Celsius. An intensive property.
Symbol: cp
Units: J/g·℃
Examples of Specific Heats1. Water 4.184 J/g·℃2. Air 1.006 J/g·℃3. Aluminum 0.900 J/g·℃4. Gold 0.129 J/g·℃5. Steel 0.470 J/g·℃
Insulator vs. ConductorSubstances with lower specific heat values
are better conductors of heat.Conductor – a material that allows the flow of
heat easily. (metals)Substances with higher specific heat values
are poor conductors of heatInsulator – a material that resists the flow of
heat (Styrofoam, rubber)
Heat EquationUsed to calculate how much energy it takes to
make a temperature change in a mass of material
E = m·cp·(T2-T1)
E = energym = mass
cp= specific heat
T2= final temperature
T1= starting temperature
Example of Using Heat Equation1. Calculate the amount of energy required to heat 15.5 g of water from 17 to 25 .℃ ℃
Another example – Let’s switch it up!2. A scientist inputs 27,500 J of thermal energy into a sample of steel. The temperature increases from 15 ℃to 75 . What is the mass of the steel?℃
Review Problem #1A 62.5-g piece of copper absorbs 6,140 J of energy when heated by a Bunsen burner. If the temperature of the copper increases from 21 °C to 310 °C, what is the specific heat of the metal?
Review Problem #2A 25.5 g sample of precious gold has an initial temperature of 15 °C. A flame transfers 378 J of thermal energy to the gold. What is the final temperature of the gold? (cp gold = 0.129 J/g· )℃
Finding Specific Heat through Energy Transfer:Remember:
The heat energy lost by one system is always gained by its surroundings!
Finding Specific Heat Problem:A hot piece of metal is dropped into 150-g of water with a starting temperature of 21 °C. The temperature of the water increased to 30 °C.1. How much energy was needed to increase the
temperature of the water?
Where did the energy come from?
2. If the metal has a mass of 47 g and a starting temperature of 200 °C, what is the specific heat of the metal?
Assume – all energy lost by metal = all energy gained by water
Assume – final temps of both are equal (thermal equilibrium)
top related