Thermal Chemistry

Question 1

exothermic

Answer 1

releasing heat
- surroundings heat up
- negative heat charge

Question 2

endothermic

Answer 2

absorbs heat
- surroundings cool down
- positive heat charge

Question 3

flat areas

Answer 3

melting/boiling

Question 4

rising areas

Answer 4

heating up H2O

Question 5

heat

Answer 5

always added, related to temperature and phase change

Question 6

q=mcp∆T

Answer 6

heating liquid

Question 7

q in q=mcp∆T

Answer 7

thermal energy (joules)

Question 8

m in q=mcp∆T

Answer 8

mass (grams)

Question 9

cp in q=mcp∆T

Answer 9

specific heat

• a constant hat varies from substance to substance
• joules per grams-kelvin (J/g˚C)
• the amount of energy required to raise 1g of a substance by 1 degrees celsius

Question 10

∆T in q=mcp∆T

Answer 10

change in temperature (kelvin or celsius)

Question 11

specific heat for identifying unknowns

Answer 11

• putting an unknown object in water allows heat to flow between the unknown and the water
• thermal equilibrium is reached when temperature becomes the same

(Tf) same for both water & object

• amount of heat gained/lost by the water is equal to the amount of heat lost/gained by unknown

Question 12

calorimetry

Answer 12

measurement of heat changes for physical and chemical processes

Question 13

calorimeter

Answer 13

measure the amount of heat absorbed or released

Question 14

Q=n*∆H fus

Answer 14

n = number of particles in moles

∆H fus = heat of fusion -> solid to liquid, positive, heat in

Question 15

Q=n*∆H vap

Answer 15

n = number of particles in moles

∆H vap= heat of vaporation -> liquid to gas, positive, heat in

Question 16

∆H values are given in either

Answer 16

Joules per mol (J/mol) or kilojoules per mole (kilo/Joules)

Question 17

when a substance changes phase

Answer 17

there Is a heat value of the change in state for each substance

Question 18

when you go up the heating curve (solid -> liquid -> gas)

Answer 18

endothermic, heat is positive

Question 19

when you go down the heating curve (gas -> liquid -> solid)

Answer 19

exothermic, heat is negative

Question 20

fus and solid

Answer 20

∆H fus = - ∆H solid

Question 21

vap and cond

Answer 21

∆H vap = - ∆H cond

Question 22

∆H fus

Answer 22

s->l
melting

Question 23

-∆H solid

Answer 23

l->s
freezing

Question 24

∆H vap

Answer 24

l->g
boiling

Question 25

-∆H cond

Answer 25

g->l
condensation

Question 26

flat part equation

Answer 26

q=mol*∆Hfus

or

q=mol*∆Hvap

Question 27

CpH2O(l)

Answer 27

4.18 J/g˚C

Question 28

energy

Answer 28

ability to do work (measured in Joules)

Question 29

potential energy

Answer 29

stored energy

Question 30

kinetic energy

Answer 30

energy of motion

Question 31

heat vs temp

Answer 31

temperature is the measure of the average kinetic
- energy of random motions of particles in a substance (measured in degrees)
- heat is the measure of the total amount of energy (measured in joules or calories)

Question 32

temperature change

Answer 32

T∆ = Tf - Ti

Question 33

∆T sign

Answer 33

• positive if temp is increasing
• negative if temp is decreasing

Question 34

heating curve states

Answer 34

solid only -> melting (solid/liquid) -> liquid only -> boiling (liquid/gas) -> gas only

Question 35

temperature change

Answer 35

solid only, liquid only, gas only

Question 36

phase change

Answer 36

melting/boiling

Question 37

heat of fusion

Answer 37

is the energy needed to melt one mole

∆Hfus occurs at melting/freezing point
- temperature stays constant!!!!

Q=(∆Hfus)(#moles)

Question 38

constant temperature (heat of fusion)

Answer 38

• solid -> liquid ∆Hfus is positive (heat in
• liquid -> solid ∆Hfus is negative (heat out)

Question 39

heat of vaporization

Answer 39

is the energy needed to boil one mole

occurs at the boiling/condensing point

Q=(∆Hvap)(#moles)

Question 40

constant temperature (heat of vaporization)

Answer 40

• liquid -> gas ∆vap is positive (heat in)
• gas -> liquid ∆vap is negative (heat out)

Question 41

heat of reaction

Answer 41

(∆Hrxn) (or enthalpy): heat energy absorbed or released during a reaction

Question 42

heat of formation

Answer 42

(∆Hf) heat energy absorbed or released, in the formation of 1 mole of a compound from its elements

Question 43

heat of solution

Answer 43

(∆Hsol): heat energy absorbed or released when a substance dissolves

Question 44

activation energy

Answer 44

Ea, energy needed to start a reaction

Question 45

activated complex

Answer 45

the unstable arrangement of atoms that exists momentarily at the peak of the activation energy

Question 46

energy diagram

Answer 46

• starts with reactants
• goes up & down in curve
• ends with products either higher or lower than before
• diff in reactants and products is ∆H

Question 47

exothermic energy diagram

Answer 47

• reactants higher than products
• reactants are less stable than products (higher energy case)
• products are more stable than products (lower energy case)

∆H rxn = product - reactants = negative

Question 48

endothermic energy diagram

Answer 48

• products higher than reactants
• reactants are more stable (lower energy state)
• products are less stable (higher energy state)

∆H rxn = product - reactants = positive

Question 49

cataylsts

Answer 49

speed up reactions by lowering the activation energy

Question 50

enthalpy

Answer 50

total energy content of a system

Question 51

enthalpy change

Answer 51

∆H
the heat energy absorbed or released in an rxn

Question 52

hess’s law

Answer 52

the total enthalpy change in a reaction

∆Hrxn = sum of Hfproducts - sum of ∆freactants

Question 53

enthalpy changes

Answer 53

1) determine ∆Hrxn for the decomposition of H2O
2) make sure equation is balanced (account 4 moles of each reactant & products)
3) look up ∆Hf for reactants and products on chart (elements are 0!)
4) solve for ∆Hrxn