Thermochemistry

Question 1

thermochemistry

Answer 1

the study of the energy involved in a reaction

Question 2

endothermic reaction

Answer 2

energy of products is more than the energy of the reactants as energy is taken in from the surroundings

Question 3

exothermic reaction

Answer 3

energy of products is less than the energy of the reactants as it looses energy to the surrounding areas
delta -

Question 4

heat of reaction

Answer 4

heat change when the numbers of moles of reactants from the balanced equation react completely

Question 5

heat of combustion

Answer 5

heat change when ONE MOLE of a substance is completely burned in excess oxygen

Question 6

if writing a balanced equation for combustion what is needed

Answer 6

reactant + O2 —–> CO2 + H2O

Question 7

what is a bomb calorimeter used for

Answer 7

measure the heat of combustion
determine the kilocalories in food

Question 8

how does a bomb calorimeter work

Answer 8

> record mass of substance being used
-> put in crucible and place inside bomb
->bomb is filled with oxygen under pressure
->this ensures complete combustion
->bomb is placed in a known quantity of water
-> temperature of water is recorded
->sample is ignited using an electrical wire
-> record rise in temperature of water
->heat produced = mass x specific heat capacity x change in temperature
->heat produced of ONE MOLE is calculated

Question 9

kilogram calorific value of a fuel

Answer 9

heat energy produced when 1 kg of the fuel is completely burned in excess oxygen

Question 10

bond energy

Answer 10

average energy required to break one mole of a particular covalent bond and to separate the neutral atoms completely from each other

Question 11

conservation of energy

Answer 11

energy is neither created nor destroyed but is changed from one form to another

Question 12

what are the steps for calculating bond energy

Answer 12

> draw out all of the separate bonds in each of the reactants and products
calculate the energy for the reactants and products seperately
minus the total of the products from the total of the reactants
if the answer is a minus number the reaction is exothermic if its positive its endothermic

Question 13

heat of neutralisation

Answer 13

heat change when one mole of H+ ions from an acid react with one Mol of OH- ions from a base

Question 14

are neutralisation reactions endo or exothermic

Answer 14

exothermic

Question 15

when is energy released small in a heat of neutralisation reaction

Answer 15

if a strong acid and weak base are used

Question 16

why is energy released small in a heat of neutralisation reaction if a strong acid and weak base are used?

Answer 16

weak acids do not fully dissociate in water
thus less OH- or H+ ions are produced so there are fewer ions available to combine thus fewer bonds are formed and less energy is given out

Question 17

what is the formula for heat released

Answer 17

H= mass(kg) x specific heat capacity x temp change

Question 18

how to calculate the heat of neutralisation from an experiment

Answer 18

1. calculate the no of moles of HCl neutralised
2. fill values into formula (mass is the mass of the acid and the base in kg)
   3.calculate the energy released if one mole of HCl was neutralised
   DONT FORGET MINUS SIGN!!!!!

Question 19

heat of formation

Answer 19

heat change that takes place when one mole of a compound in its standard state is formed from its elements in their standard state

Question 20

standard state

Answer 20

the state that the substance is in at 25 degrees C and 101 kPa

Question 21

Hess’ law

Answer 21

if a chemical reaction occurs in a number of steps, the sum of the heat changes for each step is the same as the heat change if the reaction is carried out in one step

Question 22

formula for heat of formation

Answer 22

delta H = sum of products - sum of reactants