1.4 Energetics Flashcards
What energy change is breaking bonds associated with?
Energy is taken in to break bonds —> endothermic reaction
What energy change is making bonds associated with?
Energy is released to make bonds —> exothermic reaction
What are some uses of thermochemistry?
Measuring and comparing the energy values of fuels
Calculating the energy requirements for industrial processes
Working out the theoretical amount of energy released/ taken in in a reaction
Predicting if a reaction will take place or not
What is an endothermic reaction?
One with an overall positive enthalpy change —> energy in breaking bonds> energy out making bonds
What is an exothermic reaction?
One with an overall negative enthalpy change —> energy in breaking bonds < energy out making bonds
If a reversible reaction is endothermic one way, what type of the reaction is the other way?
Exothermic
Give 2 examples of exothermic reactions
Combustion of fuels
Neutralisation
Give an example of an endothermic reaction
Thermal decomposition
Define enthalpy change; what symbol is used to represent it?
Heat energy change of a system at a constant pressure
What are the standard conditions?
100kPa/ 1atm pressure
289K / 25 degree Celsius temperture
What does in standard state mean?
The state an element/compound exists at in standard conditions (100kPa, 298K)
Draw an enthalpy change diagram for an endothermic reaction and one for an exothermic reaction
Slide 26
Define standard enthalpy of formation
The enthalpy change when one mole of a compound is formed from its constituent elements in standard conditions (100kPa, 298K) with reactants and products in their standard states
Give an example of an equation which represents standard enthalpy of formation
There are many H2 (g) +1/2O2(g) —> H2O(l)
Define standard enthalpy of combustion
The enthalpy change when one mole of a substance is burnt completely in oxygen in standard conditions (100kPa,298K) with reactants and products in their standard states