Transcript Thermochemistry - Fall River Public Schools

Chemistry
Ms. Piela
THERMOCHEMISTRY
THERMOCHEMISTRY –
 Heat
transfers in chemical
reactions
 Energy
 Definition:
The capacity to
do work or supply heat
 Basic Types: Mechanical,
Electrical, Potential, Kinetic
CHEMICAL POTENTIAL ENERGY
Energy that is stored within chemical bonds
 Determined by the arrangement and bonding of
atoms

 Examples:
Gasoline, Food, etc
EXOTHERMIC & ENDOTHERMIC
 Exothermic
Heat
processes (‘exits’)
flows out of a system
EXOTHERMIC AND ENDOTHERMIC
System loses heat (negative sign)
 Examples: Explosions!, Sun, Fire

EXOTHERMIC AND ENDOTHERMIC
 Endothermic
Heat
processes (‘enter’)
is absorbed from surroundings
EXOTHERMIC AND ENDOTHERMIC
System gains heat (positive sign), Heat change
is > 0
 Examples: Boiling water, ice melting

HEAT –
 Energy
transfers due to temperature
differences between objects
 Flows from hot to cold until temperature
equilibrium is reached
LAW OF CONSERVATION OF ENERGY –

Energy cannot be created or destroyed, only
transferred
 Can
be transformed
 Example:
Heat
Mechanical
Electrical
UNITS OF HEAT

Calorie (cal) – the amount of heat needed to
raise 1 gram of water 1 °C
 Heat
calorie is not to be confused with dietary
calories
Conversion
 1 dietary
Factor!
Woo! Calorie = 1 kcal = 1000 cal

Joule (J) – metric unit of heat and energy
CONVERSION PRACTICE

It takes 50.2 J to raise the temperature of a
100.0 g piece of glass. How many calories is
this?
CONVERSATION PRACTICE

A small chocolate bar has about 210,000
calories. How many Joules is this?
SPECIFIC HEAT –
The amount of heat required to raise 1 gram of
a substance 1 °C
 Heat capacity is the amount of heat required to
raise a substance 1 °C

SPECIFIC HEAT EQUATION
q = heat (J or cal)
 m = mass (g)
 C = specific heat J g C
 ∆T = Change in Temp. (°C)

SPECIFIC HEAT APPLICATION: LAND VS. WATER

Specific heat plays a role in buffering climates
 Specific

heat of land = 0.8 J/g ° C
 Specific heat of water = 4.184 J/g °C
How does this help buffer climates?
 Water
heats up slower and cools down
slowly, releasing heat gradually
TABLE OF SPECIFIC HEAT CAPACITIES
On the notes, you’ll see a table of specific heat
capacities for common metals.
 We’ll be using these throughout all the
problems in this section, so keep it handy!

SPECIFIC HEAT EXAMPLE 1

A 1.55 g piece of stainless steel absorbs 141 J
of heat when its temperature increases by 178
°C. What is the specific heat of stainless steel?
.511 J/g °C
SPECIFIC HEAT EXAMPLE 2

How much heat is required to raise the
temperature of 250.0 g of mercury from 52 °C
to 60 °C?
280 J
SPECIFIC HEAT EXAMPLE 3

If the initial temperature of a 10.0 g substance
is 20.0 °C and 100.0 J of heat are absorbed,
what is the final temperature? The specific heat
of the substance is 1.15 J/g °C.
28.7 °C