Energetics

Question 1

What are the standard conditions

Answer 1

pressure of 100kPa
Temp of 298K
must be in standard physical state

Question 2

what is the definition of ΔH°r

Answer 2

enthalpy change when substance in standard state react completely under standard conditions

Question 3

What is definition of ΔH°c

Answer 3

enthalpy change when mole of substance is burned completely in oxygen under standard conditions

always produce co2 and h20

Question 4

what is ΔH°neut

Answer 4

enthalpy change when acid and alkali react under standard conditions to produce one mole of water

Question 5

what is ΔH°f

Answer 5

enthalpy change when one mole of a substance is produced from its elements under standard conditions

Question 6

what happens during exothermic reactions

Answer 6

products have less energy than the reactants
Heat energy is given off by the reaction to the surroundings
The temperature of the environment increases
The energy of the system decreases

Question 7

what happens in endothermic reactions

Answer 7

products have more energy than the reactants
Heat energy is absorbed by the reaction from the surroundings
The temperature of the environment decreases
The energy of the system increases

Question 8

how can a calorimeter be made

Answer 8

polystyrene drinking cup, a vacuum flask

Question 9

what is specific heat capacity

Answer 9

energy needed to increase the temperature of 1 g of a substance by 1 oC

Question 10

what formula use to work out heat transfer

Answer 10

q = m * c * change T

Question 11

what happens to enthalpy change when rise in temp

Answer 11

the value of enthalpy change becomes negative

Question 12

three reasons why more exothermic in part b than part a

Answer 12

Heat/energy loss
(to the surroundings / to the apparatus)/
Lack of lid/no

Inaccuracy of thermometer/temperature
readings

Heat capacity is not 4.18/ the mass of
solution is not 50 g/ density of solution is
not 1 g cm-3

Question 13

what is sodium carbonate used for in cooking

Answer 13

self raising flour as co2 produced causes bread to rise

Question 14

enthalpy of hydration of ion

Answer 14

Enthalpy change when 1 mol of gaseous
ions Is dissolved/hydrated/solvated such that
further dilution causes no further heat
change

Question 15

why can you not measure enthalpy change of conversion of hydrated copper to anydrous

Answer 15

temperature change (of dehydration
reaction) cannot be measured

impossible to add exact amount of
water (to obtain value by reverse
process)

Question 16

errors in calorimeter

Answer 16

approximation in specific heat capacity of solution

reaction or dissolving may be incomplete or slow.

heat transfer (from
surroundings) (allow loss or
gain)

Question 17

how would value be different if formation of water in gaseous state

Answer 17

less exothermic as energy taken in to
form gas/energy required to form
gas/energy needed to form gas/takes
heat in to form gas/heat required to
form gas

Question 18

what is bond dissociation enthalpy

Answer 18

shortened to bond enthalpy or bond energy
energy required to break a particular bond

Question 19

if you are given enthalpy change of combustion to form hess cycle which way arrow

give the equation

Answer 19

from reactants to bottom corner and when writing intermediates write co2 and h20 balanced for each reactant

because burning substance turning into something else

Question 20

if you are given enthalpy change of formation to form hess cycle which way arrow

Answer 20

from bottom corner to reactant because form substance from the elements.