energetics

Question 1

enthalpy change

Answer 1

the heat energy change measured under conditions of constant pressure

Question 2

standard enthalpy change

Answer 2

the standard conditions (e.g 100 KPA and 298 K)

Question 3

standard enthaply of combustion

Answer 3

enthalpy change when 1 mole of a substance is completely burned in oxygen with all reactants and products in standards states under standard conditions

Question 4

standard enthalpy of formation

Answer 4

the enthalpy change when one mole of a compound is formed from its elements with all products and reactants in their standard states under standard conditions

Question 5

equations of energy change in water

Answer 5

q= mc deltat
(remember only include mass of water in equation calc)

Question 6

energy change in water (q)

Answer 6

joules

Question 7

mass of water (m)

Answer 7

grams

Question 8

SHC (c)

Answer 8

4.18

Question 9

temperature of water (delta t)

Answer 9

degrees C = K

Question 10

enthalpy equation

Answer 10

-q over n
n = number of moles
units = KJ mol -1

Question 11

hess’s law

Answer 11

states that the enthalpy change for a chemical reaction is independent of route taken

Question 12

combustion

Answer 12

arrows DOWN
co2 + h2o at bottom of triangle (always)

Question 13

formation

Answer 13

arrows UP
elements at bottom of triangle

Question 14

Explain why the value given for the O=O bond enthalpy in part (b) is not a
mean value.

Answer 14

Oxygen is the only substance that has O=O bond

Question 15

Give one reason why the bond enthalpy that you calculated in part (c) is
different from the mean bond enthalpy quoted in a data book

Answer 15

Data book value derived from (a number of) different compounds

Question 16

j to kj

Answer 16

divide by 1000