Class Notes (836,580)
Canada (509,856)
Chemistry (543)
CHEM 1A03 (173)


6 Pages
Unlock Document

David Brock

Chapter 7: Thermochemistry - Combustion or burning is a complex sequence or exothermic chemical reactions between a and an oxidant - Rapid combustion: accompanied by the production of hat or both heat and light in the form of either a glow or flames - Slow combustion: takes place at low temperatures - Respiration is an example of slow combustion - The higher the heat of combustion, the better the fuel - Hydrogen economy, methanol economy – using hydrogen / methanol to store energy - Photosynthesis is an endothermic process - Sunlight (energy) is used to build glucose and other simple sugars - 6CO2 + 6H2O  C6H2O6 + 6O2, ΔH◦ = +2.8 x 10^3 (pos because energy going in ) - Energy is extracted by combustion of the plant material - As the forward process is ENDOTHERMIC, ΔH > 0 - The reverse reaction is EXOTHERMIC, ΔH < 0 System versus Surroundings - Open system: material and energy exchange - Closed system: only energy exchange - Isolated system: neither matieral nor energy exchange Energy - Energy = the capacity to do work - Potential energy: energy of a state - Kinetic energy: energy of motion - Thermal energy: kinetic energy on a microscopic scale, movement on a molecular basis / within a molecule - Heat (q): energy transferred between a system and its surroundings as a result of a temperature gradient Heat Capacity - Heat Capacity (C): the amount of heat required to change the temperature of a system by one degree (J◦C ) or (J K ) - Water has a higher heat capacity than air – you wouldn’t last as long in the cold water vs cold air, ability to remove heat from you - Thermal energy is expressed as a molecule`s internal motions - Molecular-level complexity correlated to heat capacity; more complex, higher heat capacity - Energy available from these internal degrees of freedom contributes to a substance`s specific heat capacity - Things that are complex have higher internal degrees of freedom - Water`s high heat capacity is attributed to its bonding Defining a System`s Capacity to Store Heat - Q = m x specific heat x ΔT = C x ΔT - Heat capacity (C): the quantity of heat (q) required to change the temperature of a “system” by one degree - Specific heat capacity = “system” is 1 g of material - Molar heat capacity = “system” is 1 mol of material - 100.0g copper (specific heat = 0.385Jg-1C-1) at 100C is added to 50.0g water at 26.5C… final temp of copper-water mixture? o q(water) = -q(copper) o m(water) x c(water) x (ΔT) = - m(copper) x C(copper) x (ΔT) = 37.9 C o - Heat of Reaction – qrxn - Qrxn = the quantity of heat exchanged between a system and its surroundings when a chemical reaction occurs within the system at constant temperature - Qrxn < 0 exothermic reaction (heat produced) - Qrxn > 0 endothermic reaction (heat required) - Qsystem = 0 Bomb Calorimetry (Constant Volume): - Isolated system where heat is not transferred outside boundaries of that system and you do a reaction inside of it – reaction nside either gives off or takes in heat and we measure the physical change – temp , volume change, etc.. that we can equate back to how much energy was released or taken in by the reaction - Calorimetry – qsystem = 0 assumption. - Q calorimC calorimeterT - All energy that goes into the calorimeter sums up to zero - Qsys = qrxn + qcalorim = 0 - Qrnx = -qcalorim = -16.71 kJ (from example on slide 18) - Measured on a per mol basis Enthalpy Change, ΔH, Phase Change - When water boils or ice melts, what is the temp of the water during phase transition - Heat is required for phase transition (which occur at constant T!)  latent (hidden) heat of fusion - Molar enthalpy of fusion H2O (s) H2O(l) ΔH = 6.01kJ (at 273.15K) - Phase change = energy associated with it Differentiating Work and Heat - Familiar with ΔH  endothermic or exothermic, indicating energy required, or given off during a chemical reaction - Energy can also be input or output from a system via “work” Pressure-Volume Work, w - Explosives - Gases formed on combustion of gasoline o Chem reaction burning gasoline, releasing energy as heat and work – chem rxn explosion , rapid change in volume.. internal combustion engine? - How much work is done by an expanding gas? - Work = force x distance - W = - (m)(g)/A x Δh x A = -P ΔText - External pressure - what kind of force are we putting on the outside.. eg how much force exerted when you try to expand something - Larger your etxernal force, less work you can have done - The First law of Thermodynamics - Internal energy, U - ΔU sys
More Less

Related notes for CHEM 1A03

Log In


Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.