Energetics 1 Flashcards
What is enthalpy change?
The amount of heat energy taken in or given out during any change in a system provided the pressure is constant
What is the symbol for enthalpy?
H
What happens when an enthalpy change occurs?
- Energy is transferred between system and surroundings
- System is chemicals
- Surrounding is everything outside chemicals
What is the enthalpy change in an exothermic reaction?
Negative
Why is the enthalpy change negative for an exothermic reaction?
- Energy transferred from system to surroundings
- Products have less energy than reactants
What is the enthalpy change in an endothermic reaction?
Positive
Why is the enthalpy change negative for an endothermic reaction?
- Energy transferred from surroundings to system
- Requires an input of heat energy
- Products have more energy than reactants
What are the standard conditions?
298 K
100 kPa pressure
Solutions at 1 moldm^-3
What is the standard enthalpy change of formation of a compound?
The enthalpy change when 1 mol of the compound is formed from its elements under standard conditions
(all reactants and products being in their standard states)
What is the enthalpy change of formation of an element?
0 kJmol^-1
What is the standard enthalpy of combustion of a substance?
The enthapy change that occurs when one mole of a substance is combusted completely in oxygen under standard conditions
(all reactants and products being in their standard states)
Will incomplete combustion be less or more exothermic than complete?
Less
What is the enthaloy change of reaction?
The enthalpy change when the number of moles of reactants as specified in the balanced equation react together
