Chapter 9 Flashcards
What is the definition of enthalpy ?
Enthalpy is defined as the total heat content within a system
How to calculate enthalpy change ?
** ΔH = H(products) - H(reactants)
- because energy has to be conserved this change in energy has to be transferred, this takes place between system and your surroundings
What are exothermic reactions ?
- transfer energy to their surroundings, this can be identified be an increase in temperature of the surroundings
- ΔH = negative
What does the enthalpy and reaction profile looks like for an exothermic ?
What is an endothermic reaction?
- Energy transfer from surroundings to the system
- ΔH = positive
What does the Enthalpy and reaction profile look like for endothermic reactions ?
What are the standard conditions ?
- standard pressure: 100 kph
- standard temperature: 298K
- standard concentration: 1 mol dm-3
- standard state: the physical state of a substance under standard conditions
What is the standard enthalpy changes of a reaction ΔHr ?
enthalpy change that accompanies a reaction in the molar quantities stated in an equation, under standard conditions with all reactants and products in their standard conditions
What is the standard enthalpy changes of formulation ΔHf ?
Enthalpy change when 1 mole of a compound is formed from its elements, under standard conditions with all reactants and products in their standard state
What is the standard enthalpy change of formation of an element ?
- The formation of an element has to be 0 kj mol -1
- because you are forming an element from an element
What is standard enthalpy change of combustion ΔHc ?
Enthalpy change when 1 mole of a substance reacts completely with oxygen, under standard conditions with all reactants and products in their standard state
What is the standard enthalpy change of neutralisation ΔHneut ?
- enthalpy change that accompanies a reaction of an acid and base to form 1 mole of H2O under standard conditions with all reactants and products in their standard state
- always -57 Kj mol-1
How to calculate heat energy in a temperature change ?
- Δq = mc Δt
- where Δq is the change in energy
- m is the mass
- Δt is the change in temperature
How to determine the enthalpy change of combustion ?
- record the volume of water = surroundings (use of density to calculate
- record the mass of fuel before and after heating
- record the temperature change of the water
- use q = mct
- find the moles of fuel burnt
