enthalpy change/hess’ law

Question 1

what is standard enthalpy change?
(^T°)

Answer 1

energy change for a chemical reaction under standard conditions
l

Question 2

what’s hess’ law?

Answer 2

enthalpy change for chemical equations =sun of enthalpy changes for chem reactions producing new equation

Question 3

steps to perform hess’ law (5)

Answer 3

1. write net reaction equation
2. manipulate given equations to yield net equations
3. cancel unnecessaries + combine
4. add enthalpy changes to produce net enthalpy
5. calculate molar enthalpy

Question 4

An enthalpy change as a product=?
An enthalpy change as a reactant=?

Answer 4

exothermic heat is a product
endothermic heat is a reactant

Question 5

how do you find molar enthalpy change?

Answer 5

deltaHm= deltaH°/n

Question 6

how do you find enthalpy change?

Answer 6

deltaH= ndeltaHm OR =mdeltaHm/ M

Question 7

how to find enthalpy of formation?

Answer 7

deltaH°= products - reactants
1. find deltaH° (coefficient=moles)(elements=zero) (use standard deltaHm)
(add/subtract sig dig rules=decimalplace)

Question 8

to find moles? (two ways)

Answer 8

1. m/M
2. deltaHm/deltaH°

Question 9

ADD ON FORMATION: burning certain mass*
(2 steps)

Answer 9

1. find deltaHm = deltaH°/n (1 mol)
2. find deltaH (non-standard)

Question 10

prerequisites of chemical reactions (2)

Answer 10

1. activation energy (Ea) -initial spark that starts reaction, reactants must collide to break chem. bonds
2. orientation- all matters is constantly moving (translating A-B, vibrating, rotating) - chem. bonds will only form if particles are lined up correctly

Question 11

what are catalysts?

Answer 11

they reduce Ea by changing the reaction mechanism (pathway that reaction follows)
don’t always change enthalpy

Question 12

what are enzymes?
(3 types)

Answer 12

biological catalysts that reduce Ea for biological reactions
1. protease- break down protein
2. lipase- break down lipids
3. amylase- break down carbs/starches

Question 13

what is bond energy?

Answer 13

energy that is stored for chem. bonds & the amount of heat needed to break bond

Question 14

exo or endo?
bond breakage & formation

Answer 14

bond breakage= endo
bond formation=exo

Question 15

three mechanisms of heat transfer?
( + their meaning)

Answer 15

1. conduction- direct contact
2. convection- circulating fluid
3. radiation- electromagnetic waves (doesn’t require medium)

Question 16

what are the three energy demands?
(+ their meaning)

Answer 16

1. residential- natural gas
2. industrial- coal
3. transportation- gas/diesel/jet fuel(hydrocarbons)

Question 17

energy sources: solar & non solar (4 each)

Answer 17

solar: solar panels, wind, hydroelectricity, fossil fuels
non solar: batteries, tidal, geothermal, nuclear