save my exams energetics

Question 1

why enthalpy changes take place

Answer 1

because bonds are being broken and formed
Energy is needed to overcome attractive forces between atoms

Question 2

bond breaking exo and endo

Answer 2

endothermic

Question 3

bon forming is exo or endo

Answer 3

Energy is released from the reaction to the surroundings (in the form of heat) when new bonds are formed
therefore exothermic

Question 4

what determines whether the reaction is overall exothermic or endothermic

Answer 4

The sum of the energy in and energy out

Question 5

endothermic

Answer 5

If more energy is required to break bonds than energy is released when new bonds are formed

Question 6

exothermic

Answer 6

more energy is released when new bonds are formed than energy is required to break bonds

Question 7

energy level diagram i

Answer 7

hows the energies of the reactants, the transition state(s) and the products of the reaction as the reaction proceeds

Question 8

transition state

Answer 8

stage during the reaction at which chemical bonds are partially broken and formed

Question 9

why transtion state is unstable

Answer 9

a molecule in the transition state cannot be isolated and is higher in energy than the reactants and products

Question 10

activation energy

Answer 10

nergy needed to reach the transition state
he minimum amount of energy needed for reactant molecules to have a successful collision and start the reaction’

Question 11

exo diagram

Answer 11

eactants are higher in energy than the products
eactants are therefore closer in energy to the transition state
exothermic reactions have a lower activation energy compared to endothermic reactions

Question 12

endo diagram

Answer 12

reactants are lower in energy than the products
therefore further away in energy to the transition state
This means that endothermc reactions have a higher activation energy compared to exothermic reactions

Question 13

enthalpy

Answer 13

total chemical energy inside a substance

Question 14

enthalpy change symbol

Answer 14

ΔH (
pos or neg

Question 15

temp of ev in exo

Answer 15

Heat energy is given off by the reaction to the surroundings
The temperature of the environment increases - this can be measured with a thermometer
The energy of the system decreases
enthalpy decrease
negative

Question 16

why exo is thermodynamically possible

Answer 16

because the enthalpy of the reactants is higher than that of the products

Question 17

endo environment

Answer 17

The temperature of the environment decreases - this can be measured with a thermometer
The energy of the system increases
enthalpy increase
positive

Question 18

standard enthalpy conditions

Answer 18

pressure of 100 kPa
A temperature of 298 K (25 oC)
standard physical state (solid, liquid or gas)

Question 19

the standard enthalpy change symbol

Answer 19

ΔHꝊ

Question 20

reaction

Answer 20

enthlpy change when reactants in stoichiometric equtaion recat to give products under standard conditions

Question 21

formation

Answer 21

the enthalpy change when one mole of a compound is formed fom its elements under sdtandard conditions

Question 22

combustions

Answer 22

enthalpy change when one mole of a substance is burnnt inexcess oxygen under standard condtions

Question 23

neutralisation

Answer 23

enthalpy change when one mole of water is formed by reacing acid and alkali undee standard conditions

Question 24

reac tion exo or endo

Answer 24

both

Question 25

formation exo and endo

Answer 25

both

Question 26

combustion exo or endo

Answer 26

exo

Question 27

neutralisation exo or endo

Answer 27

exo

Question 28

calorimetry

Answer 28

measurement enthalpy changes in chemical reactions

Question 29

how to make calorimeter

Answer 29

polystyrene drinking cup, a vacuum flask or metal can

Question 30

specific heat capacity

Answer 30

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

Question 31

spec heat cap of water

Answer 31

4.18 J g-1 oC-1

Question 32

energy transferred

Answer 32

q=mcxdelta t

Question 33

bond dissociation energy

Answer 33

The amount of energy required to break one mole of a specific covalent bond in the gas phase
bond energy or bond enthalpy

Question 34

Average bond energy

Answer 34

Bond energies are affected by other atoms in the molecule (the environment)
Therefore, an average of a number of the same type of bond but in different environments is calculated

Question 35

mean bond enthalpies

Answer 35

average values over a range of compounds