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