Energetics

Question 1

exothermic definition

Answer 1

reaction that releases energy to the surrounding
(negative enthalpy change)

Question 2

exothermic reaction example

Answer 2

combustion
neutralisation

Question 3

endothermic reaction definition

Answer 3

reaction that absorbs energy from surroundings
(positive enthalpy change)

Question 4

endothermic reactions example

Answer 4

thermal decomposition
photosynthesis

Question 5

enthalpy change definition

Answer 5

heat energy change at constant pressure
(KJmol-1)

Question 6

standard conditions

Answer 6

100 kPa
298 Kelvin (25 degrees celsius)
1moldm-3

Question 7

enthalpy change of formation definition

Answer 7

energy change when one mole of a substance is formed from its constituent elements
under standard conditions

Question 8

enthalpy change of combustion

Answer 8

enthalpy change when one mole of a substance is completely burned in excess o2
under standard conditions

Question 9

enthalpy change of neutralisation

Answer 9

enthalpy change when one mole of water is formed from a reaction between an alkali and acid
under standard conditions

Question 10

hess’s law definition

Answer 10

total enthalpy change of a reaction is independent of the route taken
providing the initial and final conditions are the same

Question 11

bond enthalpy

Answer 11

enthalpy change required to break one mole
of a bond in its gaseous state

Question 12

mean bond enthalpy

Answer 12

averaged enthalpy required to break one mole of a bond
averaged over different molecules

Question 13

specific heat capacity

Answer 13

the amount of energy needed to raise 1g of a substance by 1K
(4.18 J g-1 K-1)

Question 14

Standard enthalpy of formation equation

Answer 14

Enthalpy = -(products) + reactants

Question 15

Enthalpy of combustion equation

Answer 15

Enthalpy = reactants - products

Question 16

Enthalpy equation

Answer 16

Step1:
q = M C T
q (energy) in joules
M (mass) in grams
C (shc) is 4.18Jg-1K-1
T (temp change) in Kelvin or degrees
Step 2:
Q/1000 = Kj
Step 3:
Enthalpy = Kj / number of mols

Question 17

Cycle arrows in formation equation

Answer 17

Goes upwards from constituent elements to reactants and products

Question 18

Arrows in combustion

Answer 18

Goes downwards to constituent elements

Question 19

Endothermic graphs

Answer 19

Go end up higher as they gain energy from aurroundinga

Question 20

Exothermic graph

Answer 20

Go end up lower as they lose energy to surroundings

Question 21

Conversion between kelvin and Celsius

Answer 21

Kelvin = C + 273
Celsius = K - 273