CH4 Energetics Flashcards
What reaction is associated with breaking bonds
Endothermic reaction
What reaction is associated with making bonds
Exothermic reaction
What is an endothermic reaction
A reaction with a positive enthalpy change
More breaking bonds thn making bonds
What is an exothermic reaction
A reaction with a negative enthalpy change
More making bonds than breaking bonds
2 examples of exothermic reactions
Combustion of fuels
Neutralisation
Example of endothermic reaction
Thermal decomposition
Definition and symbol of enthalpy change
Energy change of a system at a constant pressure
ΔH
What are standard conditions
100kPa and 298K
Standard enthalpy of formation
The enthalpy change when 1 mole of a compound is formed from its constituent elements in standard conditions, with reactants and products in their standard states
Standard enthalpy of combustion
The enthalpy change when 1 mole of a substance is burnt completely in oxygen in standard conditions, with reactants and products in their standard states
How to calculate enthalpy change from experimental data
Q = mcΔT
m - mass of substance being heated
c - specific heat capacity of that substance
ΔT - change in temperature
What is a flame calorimeter: how is it different to a simple calorimeter
Reduces heat lost to the surroundings to give more accurate results: has a spiral chimney made of copper, an enclosed flame and fuel burnt in pure oxygen
Hess’ Law
The enthalpy change for a reaction is the same regardless of the route taken
What is the enthalpy of an element
Enthalpy of all elements in their standard states is defined as 0
Bond dissociation enthalpy
Enthalpy change required to break a covalent bond, with all species in the gaseous state
