7.1. Energetics 1

Question 1

temperature

Answer 1

measure of the average kinetic E of particles in a system - state function - expressed in °C or K

Question 2

heat

Answer 2

energy in transfer - expressed in J or kJ

Question 3

enthalpy change (delta H)

Answer 3

heat transferred from a closed system to the surroundings during a chemical reaction

Question 4

exothermic vs endothermic reaction (give examples of each)

Answer 4

exo is when heat is released from the system and endo is when it is absorbed by the system
combustion of fuels, acid-base neutralization
formation of NO2, reaction of Ba(OH)2 and NH4Cl

Question 5

draw and annotate graphs of exo and endo reaction

Answer 5

…

Question 6

calorimeter

Answer 6

used to measure the actual amount of heat evolved in an exothermic reaction by using he heat released to increase the temperature of a known mass of water

Question 7

assumptions and errors using a calorimeter

Answer 7

assumptions:
1) the heat released is completely transferred to water
2) calorimeter is an insulator so its c is zero
3) T max reached is equal to heta evolved
4) C(aqueous solution) = C(water)
errors:
1) loss of heat (graph)

Question 8

formula for heat

Answer 8

Q=mc(delta)T
c=heat capacity

Question 9

bond enthalpy
(+ formula)

Answer 9

E change when one mole of a covalent bond in the gaseous state is formed from its gaseous atoms
BE = input - output
(bonds broken - bonds formed)

Question 10

forming bonds is…
breaking bonds is…

Answer 10

exothermic
endothermic

Question 11

limitations of using bond enthalpies

Answer 11

1) all reactants have to be in gaseous form
2) average bond enthalpies are used

Question 12

Hess’ law

Answer 12

the heat of a whole reaction is equivalent to the sum of its steps (adding equations)

Question 13

combustion of:

Answer 13

• metals
• non-metals
• complete combustion of organic compounds
• incomplete combustion of organic compounds (in the absence of sufficient oxygen - CO and carbon soot produced)

Question 14

what is choice of fuel determined by

Answer 14

the fuel’s specific energy:
E(specific) = (E released from the fuel)/(m of fuel consumed)

Question 15

fossil fuels

Answer 15

• crude oil, coal, and natural gas
• unrenewable E sources
• produce greenhouse gases (CO2)

Question 16

biofuels

Answer 16

• renewable E sources
  1) direct combustion of plant material
  2) biogas (methane and CO2 mixture)
  3) fermentation to produce ethanol
• biological carbon fixation - production of organic compounds from CO2 (photosynthesis)

Question 17

fuel cells

Answer 17

hydrogen fuel cell
- converts chemical E directly to electrical E - doesn’t need an external source of E for charging

Question 18

standard enthalpy change of reaction

Answer 18

the enthalpy change when molar quantities of reactants in their normal states react to form products in their normal states under standard conditions of T and p (25 °C and 1 atm, when element is in its most stable form (O2(g)))

Question 19

(delta)H<0
(delta)H>0

Answer 19

exothermic
endothermic

Question 20

standard molar enthalpy of formation

Answer 20

the enthalpy change for the formation of one mole of a substance from its elements in their standard states - (delta)Hf
its value is zero for all free elements (when only on element is present)