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