What is the difference between heat and temperature? HEAT is energy that transfers from one

object/substance to another

TEMPERATURE is a measure of the amount of energy an object/substance has

A. Energy Transformations Energy that is stored in the chemical

bonds of a substance is called CHEMICAL POTENTIAL ENERGY

Heat ALWAYS flows from hot to cold

B. Endothermic and Exothermic Processes

System=the reaction Surroundings=everything around the

reaction

Surroundings

Law of Conservation of Energy- energy can be neither created nor destroyed

System

B. Endothermic and Exothermic Processes

Endothermic Process- heat is absorbed from the surroundingsEndo = Into

Endothermic processes are represented by a positive “q”

HEAT

B. Endothermic and Exothermic Processes

Exothermic process- heat is released into the surroundingsExo = Exit

Exothermic processes are represented by a negative “q”

HEAT

C. Measuring Heat Flow

Two Common UnitsJoulecalorie

1J = 0.2390 cal

4.184 J = 1 cal

1Calorie = 1 kilocal = 1000 cal

D. Heat Capacity and Specific Heat

Heat Capacity depends on:The mass of the objectThe chemical composition of the object

“the amount of heat needed to increase the temperature of an object by 1 oC

Specific heat capacity- amount of heat needed to raise the temperature of 1g by 1 oC

D. Heat Capacity and Specific Heat

C = q / (m X ΔT)

C =Specific Heat q = heat (joules or calories) m = mass (grams) ΔT = change in temperature

The change in temperature can be measure in Kelvin or degrees Celsius

The temperature of a 95.4g piece of copper increases from 25.0 oC to 48.0 oC when it absorbs 849 J of heat. What is the specific heat of copper?

Known:

m= 95.4g

q=849 J

ΔT= 48.0-25.0=23.0 oC

Work:

C= 849J/ (95.4g)(23.0 oC) = 0.387 J/(g· oC)

E. Calorimetry

Measures the heat flow into or out of a system

Heat released by the system is equal to heat absorbed by the surroundings

ENTHALPY: (H) the heat constant of a system at constant pressure

E. Calorimetry

The terms heat and enthalpy change are interchangeableq = ΔH

qsys = ΔH = -m x C x ΔT

Negative enthalpy = exothermicPositive enthalpy = endothermic

When 25.0mL of water containing HCl at 25.0 oC is added to 25.0mL of water containing NaOH at 25.0 oC in a calorimeter a rxn occurs. Calculate the enthalpy change (in kJ) during the rxn if the highest temperature observed was 32.0 oC. Assume all densities =1g/mL

KNOWN:

Cwater=4.18J/g oC

V=25.0mL+25.0mL

ΔT=7 oC

Density= 1g/mL

ΔH = ?

m= (50mL) x (1.00g/mL) = 50g

ΔT= TF – Ti = 32.0 – 25.0 =7.0

ΔH= -mCΔT= -(50.0g)(4.18J/goC)(7.0oC)

ΔH= -1463 J = -1500J = -1.5kJ

F. Thermochemical Equations In a thermochemical equation, the

enthalpy of change for the reaction can be written as either a reactant or a product

Endothermic (positive ΔH)2NaHCO3 + 129kJ Na2CO3 + H2O + CO2

Exothermic (negative ΔH)CaO + H2O Ca(OH)2 + 65.2kJ

G. Heat of Combustion

The heat of reaction for the complete burning of one mole of a substance

Written the same was as change in enthalpy

Write the thermochemical equation for the oxidation of Iron (III) if its

ΔH= -1652 kJ

Fe(s) + O2(g)→ Fe2O3(s) + 1652

How much heat is evolved when 10.00g of Iron is reacted with excess oxygen?

4 3 2

10.00g Fe

55.85g Fe

1 mol= 0.1791 mol Fe

0.1791 mol Fe

4 mol Fe

1652 kJ =73.97 kJ of heat