Energetics 4

Question 1

the amount of energy involved when a chemical reaction takes place is important for many reasons

Answer 1

• energy values of fuels
• energy require for industrial processes
• the theoretical amount of energy to break bonds and amount of energy released when bonds are made
• predict whether a reaction will take place

Question 2

exothermic

Answer 2

energy has been given out

neutralising acids

Question 3

endothermic

Answer 3

energy is taken in

breakdown of limestone

Question 4

standard conditions for measuring enthalpy changes

Answer 4

pressure 100kPa

temperature 298K

Question 5

physical states of the reactants and products

Answer 5

physical states affect the enthalpy change like energy is needed to change a liquid into a gas

Question 6

standard molar enthalpy of formation

Answer 6

enthalpy change when one mole of substance is formed from its constituent elements under standard conditions, all reactants and products being in their standard states.

An element formation energy is zero

Question 7

standard molar enthalpy of combustion

Answer 7

enthalpy change when one mole of a substance is completely burnt in oxygen under standard conditions, all reactants and products being in their standard states

Question 8

temperature

Answer 8

is related to the average kinetic energy of the particles in a system.

Question 9

heat

Answer 9

a measure of the total energy of all the particles present in a given amount of substance.
flows to a high temperature to low temperature

Question 10

measuring an enthalpy change of a reaction

Answer 10

• mass of a substance that is being heated up or cooled down
• temperature change
• specific heat capacity of the substance

Question 11

specific heat capacity

Answer 11

the amount of heat needed to raise the temperature of 1g of substance by 1K

Question 12

simple calorimeter

Answer 12

burn the fuel to heat a known mass of water and then measure the temperture rise of the water.

Question 13

flame calorimeter

Answer 13

reduce heat loss

• the spiral chimney is made of copper
• flame is enclosed
• fuel burns in pure oxygen rather than air

Question 14

displacement reactions

Answer 14

metal is more reactive than another will displace a less reactive one from the compound

Question 15

Hess’s law

Answer 15

Hess’s law states that the enthalpy change for a chemical reaction is the same, whatever route is taken from reactants to products

Question 16

enthalpy changes of formation

Answer 16

H1 = H2+H3

🔺H = breaking bonds - forming bonds

Question 17

Standard conditions

Answer 17

Pressure 100kPa ( normal atmospheric pressure)
Temperature 298k (normal room temperature)

Question 18

Specific heat capacity equations

Answer 18

Q = mc🔺T

Question 19

Enthalpy of neutralisation

Answer 19

The enthalpy change during neutralisation with an acid and an alkali to form one mole of water

Question 20

Enthalpy change of displacement

Answer 20

A metal that is more reactive than another will displace the less reactive one from a compound. If the compound will dissolve in water, this reaction can be investigated using a polystyrene breaker as before

Question 21

Formation arrows

Answer 21

Elements to reactants

Question 22

Combustion arrows

Answer 22

Reactants to elements

Question 23

Mean bond enthalpy

Answer 23

Average value of the bond dissociated enthalpy for a given type of bond taken from a range of different compounds

Question 24

Bond dissociation enthalpy

Answer 24

Enthalpy change required to break a covalent bond with all species in the gases

Question 25

Bond enthalpies methane

Answer 25

If the bonds in methane are broken one at a time, the energy required is not the same fro each bond

Question 26

Enthalpy change (∆H)

Answer 26

Enthalpy change (∆H) is the heat energy change measured under conditions of constant pressure.