Chapter 9 Flashcards
What is enthalpy meaning
H, a measure of heat energy in a chemical System
- can’t be measured but change can
What formula for enthalpy change
Enthalpy PRODUCTS - REACTANTS
what is conservation of energy and how used
Energy cannot be created or destroyed
Energy transferred or gained by reactions is gained or transferred by surroundings here
Exothermic = what, endothermic = what
Exothermic = drop, energy transferred from reaction to surroundings, increase temp, negative change
Endothermic = increase of graph , energy transferred from surrounding ti reaction , temp decrease, positive
What is activation energy
The minimum amount of energy required forma reaction to take place
What is standard conditions and why used!
Chemists use a standard of conditions so that reactions can be compared, snd they are close to typical working conditions .
Denoted by the circle with line at top, means enthalpy change under standard conditions
What are 4 standard Codntioms and their values
1) pressure = 100kpa
2) temperature = 25°, 298k
3) concentration (for solutions) = 1moldm^-3
4) state = whatever the state is at at 100kpa and 298k?
What is the standard enthalpy change of reaction and what about moles?
Just the enthalpy change of a reaction in standard conditions
Triangle r H °
- given by KJ/ mol, of a reaction . If balancing moles are multiplied by 2, then so is enthalpy change
What is the standard enthalpy change of FORMATION
What to look out for?
triangle f H°
The enthalpy change takes place when one MOLE of a COMPOUND is formed from its elements , UNDER STANDARD CONDITIONS
As a result of you making MGO, it has to be ONE MOLE of MgO, so you need enthalpy change where it gives this even if balancing numbers are in 1/2 or something
What is the standard enthalpy change of formation for just an element?
Making one mole of an element from it’d element required no change= so enthalpy for all elements , have an enthalpy change of formation of just 0
Standard enthalpy change of combustion ?
What is it and where is the one
Is the enthalpy change that takes place when ONE MOLE of a substance reacts completely with oxygen (no matter how many mol) under STANDARD CONDITIONS!
- so 1 mole c4h10 with like 7 mol oxygen is correct , gives different mole product calm
Standard enthalpy change of neutralisation?
What to look out for?
Is the enthalpy change that accompanied the reaction of an acid by a base to form ONE MOLE OF H20 UNDER STANDARD CONDITIONS
1 has to be the water
As a result it is H+ + OH- —> H2O, -57kj / mol
Here Esch reaction will involve one h + and one oh-, so the standard enthalpy change of neutralisation will be THE SAME FOR ALL REACTIONS
Where does the one go for everything
1) formation
2) combustion
3) neutralisation
1) product compound
2) reactant reacting with oxygen
3) water produced
Kelvin conversion
0k = absolute 0 = -273° so 0°= 273k
How do we technically measure the temperature change of surroundings ?
- thermometer is part of surroundings co change in temp here = change in temp