Beaker with hot water
17
Beaker with hot water Exothermic Exothermic “ “ exiting heat” exiting from exiting heat” exiting from ______ you were the beaker, you sense_______ cool cool If you were the hand, you sense______ warm warm the the water/beaker water/beaker
description
Beaker with hot water. Exothermic “exiting heat” exiting from ______. the water/beaker. warm. If you were the hand, you sense______. If you were the beaker, you sense_________. cool. Beaker with cold water. Endothermic “entering heat” entering from _. the hand. - PowerPoint PPT Presentation
Transcript of Beaker with hot water
Beaker with hot water
ExothermicExothermic ““exiting heat” exiting fromexiting heat” exiting from ______
If you were the beaker, you sense_________coolcoolcoolcoolIf you were the hand, you sense______warmwarm
the water/beakerthe water/beaker
Beaker with cold water
Endothermic “entering heat” Endothermic “entering heat” entering from _ entering from _
If you were the beaker, you sense______If you were the hand you sense _______
_warmwarm_____coolcoolcoolcool
the handthe hand
What changes happen using this size beaker?
Primary Factors
Mass
Temperature
NOTICE
Heat that flows includes temperature,
but is not the same as temperature.
Symbolsm = mass
T = temperature
q = heat flow (- = out, + = in)
c = specific heat(ability of pure
substance to retain heat)C = heat capacity(ability of
object to retain heat)
Mathematical Relationships
q = m x c x ΔΤ
q = C x ΔΤ
Hot metal warms the waterMetal transfers heat to
waterWater gains heat from metalMetal heat loss
equals water heat gain
Symbolic Expression
-q(metal) = q (water)
-(mxcxΔΤ (metal)=(mxcxΔΤ
(water)
BEYOND CALORIMETRY
ENERGY CHANGES IN REACTIONSENERGY CHANGES IN REACTIONS
ENTHALPY SYMBOL HENTHALPY SYMBOL H
ENTHALPY CHANGE ENTHALPY CHANGE ΔΔ H H
Remember???
ExothermicExothermic - - ΔΔHH
Remember??
Endothermic Endothermic ΔΔHH
Thermochemical Equations
H2(g) + Cl2(g) →2 HCl(g) ΔH = - 185
kJNOTICE:
phases must be includedcoefficients represents molessign of ΔH indicates direction of heat flowproducts, reactants assumed to be 25 oC
Thermochemical Rules
size ofΔH directly proportional to moles
ΔH for reverse reaction - opposite sign
ΔH same regardless of number of steps
Standard Enthalpy of Formation
Can predict heat flow for ANY equation
Symbol - ΔHo
1 atm, 1 M and 25 oC
f
Calculating Standard Enthalpies
ΔHo = ∑ΔHo products - ∑ΔHo reactantsf f
Elements in standard state - omitted
Must take coefficients into account
Practice #24 page 221
First Law of Thermodynamics-“total energy of a system is the sum of all energy and work going into and out of that system”.
ΔE(system) = -ΔE(surroundings) ΔE = q + wheat work
system
q
-q -w
w
