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)