1.4 Energetics Flashcards
What type of reaction is breaking bonds
Endothermic (energy is taken in).
What type of reaction is forming bonds
Exothermic (energy is released).
How can you tell from the enthalpy change if a reaction is exothermic or endothermic
- If the enthalpy change is negative, the reaction is exothermic
- If the enthalpy change is positive, the reaction is endothermic
What is the equation used to calculate the enthalpy change of a reaction
△H = energy to break bonds - energy to make bonds
What are ‘standard conditions’
- 100kPa pressure
- 298K (or 25 degrees)
What is enthalpy of formation
The enthalpy change when one mole of a substance is produced from its elements in their standard states under standard conditions.
What is enthalpy of combustion
The enthalpy change when one mole of a substance is burned completely in oxygen under standard conditions.
What is calorimetry
An experimental method for finding the enthalpy change by measuring temperature change over time.
What is the equation used to calculate the energy change (q)
- q = mc△T
- q is the energy change
- m is the mass in grams
- c is the specific heat capacity
- △T is the temperature change
What is specific heat capacity
The energy required to raise the temperature of 1g of a substance by 1K with no change in state.
How do you calculate the enthalpy change using the energy change (q)
△H = q/moles
What is Hess’s law
The enthalpy change of a reaction is independent of the route taken.
Which way do the arrow point in a Hess’s law cycle for calculating enthalpy of formation
Point out from the middle
Which way do the arrow point in a Hess’s law cycle for calculating enthalpy of combustion
Point towards the middle
What is bond enthalpy
The energy required to break one mole of the stated bond in a gaseous state under standard conditions.
