3.2.1- Enthalpy Changes

Question 1

What are the standard conditions?

Answer 1

100kPa pressure
298 K temperature

Question 2

What happens when energy is taken in from the surroundings?

Answer 2

The reaction is endothermic, and the enthalpy change is positive

Question 3

How do you calculate overall enthalpy change?

Answer 3

Energy to break bonds- energy released by making bonds

Question 4

What is activation energy?

Answer 4

The minimum energy required for a reaction to take place between two colliding reactant particles

Question 5

What is the enthalpy change of reaction?

Answer 5

The enthalpy change associated with a stated reaction under standard conditions

Question 6

What is enthalpy change of formation?

Answer 6

The enthalpy change when one mole of a substance is produced from its elements in their standard states under standard conditions

Question 7

What is the enthalpy change of combustion?

Answer 7

The enthalpy change when one mole of a substance is burned completely in oxygen under standard conditions

Question 8

What is the enthalpy change of neutralisation?

Answer 8

The enthalpy change when solutions of acid and alkali react together under standard conditions to produce one mole of water

Question 9

What is calorimetry?

Answer 9

An experimental method for finding enthalpy change, which works by measuring temperature change over time

Question 10

What is specific heat capacity?

Answer 10

The energy required to raise 1g of substance by 1K without a change of state

Question 11

What is the equation for energy change?

Answer 11

q=mc*temp change

Question 12

What sources of error are there for calorimetry?

Answer 12

-values are never completely accurate since energy is easily lost from the system
-shc is taken to be 4.18, which is the value for water and not the actual solution
-the shc of the calorimeter isn’t taken into account

Question 13

What is bond enthalpy data?

Answer 13

The energy required to break one mole of the stated bond in a gaseous state, under standard conditions

Question 14

What can be done to prevent heat being lost in calorimetry?

Answer 14

Put a lid on the calorimeter and insulate the outsides of the calorimeter

Question 15

What is Hess’s law?

Answer 15

Energy in a reaction system must be conserved as energy can’t be created or destroyed, so the overall enthalpy change for a reaction is the same regardless of the route taken

Question 16

What way do the arrows point for Hess’s law for enthalpy of formation?

Answer 16

Point out/up from the central elements

Question 17

What way do the arrows point for Hess’s law for enthalpy of combustion?

Answer 17

Point towards the central products which always include H2O and CO2