energetics(both)

Question 1

what are the standard conditions?

Answer 1

100kpa
298k

Question 2

what is a formation reaction?

Answer 2

when one mole of a substance is formed from its constituent elements

Question 3

give the formation reaction for ammonia

Answer 3

1/2N2+ 1 1/2 H2= NH3

Question 4

define enthalpy change

Answer 4

heat energychange of a reaction at constant pressure

Question 5

what are the two elements that are liquid under standard condtions?

Answer 5

• bromine
• mercury

Question 6

how do you calculate the enthalpy change using mean bond enthalpy?

Answer 6

total energy to break bonds- total energy released from forming bonds

Question 7

define mean bond enthalpy

Answer 7

an average value for the bond enthlpy of a particular bond over the range of compounds it is found in

Question 8

what is calorimetry used for?

Answer 8

enthalpy change of combustion

Question 9

what is the units for enthalpy change

Answer 9

KJmoldm3

Question 10

what calculation is used to work out the energy from a calorimetry experiment?

Answer 10

q=mc deltaT

Question 11

what are the different components of the q= mc delta T equation+give units

Answer 11

q= heat energy lost/gained J
m= mass of water/solution being heated
c= SHC of water g-1K-1
t=temperature change K

Question 12

100g of water was heated from 23 degrees to 57 degrees by 1.8g of ethanol. calc the energy transferred and hence the enthalpy change of the fuel

Answer 12

14212J or 14.212KJ=q
enthalpy= q/moles
enthalpy=-364.4KJmol-1

Question 13

what can calorimetry be used for?

Answer 13

calculating energy change from a calorimetry experiment of a solution or fuel

Question 14

What is the units for Enthalpy?

Answer 14

KJmoldm-3

Question 15

Why is it important during RP 2 that the mixture is stirred before recording each temperature

Answer 15

Ensure all solution is at the same temperature to give an accurate reading

Question 16

what is hesss law?

Answer 16

the total enthalpy change of a reaction is independent of the route taken

Question 17

draw the formation cycle

Question 18

draw the enthalpy of combustion cycle

Question 19

what do you do during hess’ cycles if there is reactants and products that are exactly the same and the same amount of moles

Answer 19

do not need to include these in the calculation because they will cancel each other out

Question 20

how do you check if your hess’ cycle calculations are correct?

Answer 20

go along the cycle and add all values it should add to 0

Question 21

what is the calculation for enthalpy change?

Answer 21

total energy absorbed- total energy released

Question 22

define standard enthalpy of combustion

Answer 22

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

Question 23

define standard enthalpy of formation

Answer 23

enthalpy change when 1 mole of a compound is formed from its constituent elements with all reactants and products
in their standard states under standard conditions

Question 23

define standard enthalpy change of reaction

Answer 23

the enthalpy change when a reaction occurs in molar quantities shown in the chemical equation under standard conditions with all reactants and products in their standard states

Question 24

other than heat loss why may the enthalpy of combustion determined experimentsally be less exothermic then calculated using enthalpies of formation?

Answer 24

incomplete combustion, experiment not completed under SC

Question 25

how many double bonds and single bonds do these contain: water, carbon dioxide, oxygen

Answer 25

water= 2 single
carbon dioxide=2 double
oxygen=1 double

Question 26

what is the gibbs free energy equation

Question 27

give the units of the aspects in gibbs free energy

Answer 27

gibbs free energy =Jmol-1
enthalpy chnage=jmol-1dm3
enthalpy of the system=Jk-1mol-1