Energetics - TN

Question 1

what is the enthalpy change of a reaction

Answer 1

the heat energy it releases or absorbs per mole

Question 2

what is the symbol for enthalpy change

Answer 2

Question 3

units of enthalpy change

Answer 3

kJ / mol

Question 4

what is a positive enthalpy change

Answer 4

• endothermic
• when heat energy is absorbed
• when breaking bonds

Question 5

what is a negative enthalpy change

Answer 5

• exothermic
• heat is released
• when bonds are created

Question 6

exothermic energy level diagram

Answer 6

heat is RELEASED to surroundings so LOST from the reactants

Question 7

total enthalpy change =

Answer 7

energy from bonds broken - energy from bonds created

Question 8

reaction profile diagram for an exothermic reaction

Answer 8

• heat energy is absorbed, then lost as bonds are broken then created

Question 9

what does a reaction profile diagram show

Answer 9

the path the reaction actually takes from the reactants to the products

Question 10

what is the activation energy on a reaction profile diagram

Answer 10

it is the energy needed to break the bonds and is shown by an arrow from the reactants up to the top of the hump

Question 11

what needs to happen to bonds to create an exothermic reaction

Answer 11

bond making - heat energy released

Question 12

what needs to happen to bonds to create an endothermic reaction

Answer 12

bond breaking - heat energy absorbed

Question 13

what is bond energy

Answer 13

the amount of energy that is absorbed or released when bonds are broken or made

Question 14

how to calculate enthalpy change

Answer 14

bonds broken - bonds made

Question 15

draw a reaction profile diagram for an exothermic reaction

Answer 15

Question 16

what is calorimetry

Answer 16

an experimental method used to measure enthalpy change

Question 17

explain the observations of an exothermic reaction

Answer 17

Question 18

formula for the amount of heat energy in Joules released in an experiment

Answer 18

energy = (mass of water or solution being heated by the fuel) x (specific heat capacity of water - 4.18J/kg*C) x (change in temp of water)

Question 19

what is a positive enthalpy change

Answer 19

when heat is taken into a substance

Question 20

what is the equation for enthalpy change

Answer 20

(-energy / 1000) / moles

Question 21

what is the unit for enthalpy change

Answer 21

kJ/mol

Question 22

why would the calculated enthalpy change be different to the experimental enthalpy change

Answer 22

• heat lost to surroundings
• incomplete combustion

also for solution calorimetry - the water being heated is not longer pure water as it has things dissolved in it. this means its specific heat capacity is no longer exactly 4.18

Question 23

how to carry out combustion calorimetry

Answer 23

• weigh out 50g water and place above the burner
• measure initial mass of burner and temp of water
• ignite the burner, stir water for 30secs then extinguish the burner
• measure the final mass of the burner and the maximum temperature of the water

Question 24

what are the two types of calorimetry

Answer 24

combustion calorimetry and solution calorimetry

Question 25

how to carry out a solution calorimetry

Answer 25

measuring the enthalpy change for the displacement reaction between Mg and CuSO4

• measure out 25cm3 CuSO4 into a polystyrene cup
• measure initial temp
• add 1g Mg and stir continuously
• measure the maximum temp of the solution