Topic 7: Thermo Chemistry Flashcards
What is ΔH?
Change in Enthalpy.
What is an exothermic reaction?
Exothermic reactions transfer energy to the surroundings.
What is an endothermic reaction?
Endothermic reactions take energy in from the surroundings.
How do you know if the reaction is exothermic or endothermic?
If there is -ΔH the reaction is exothermic.
If there is +ΔH the reaction is endothermic.
How to draw an energy level diagram?
LOOK IN BOOK.
Burning Alcohols experiment?
LOOK IN BOOK
Alcohols equation?
(alcohol) + oxygen = carbon dioxide + water
Burning Alcohol experiment, calculations?
- Write word equation
- Write symbol equation and structure
- Calculate Bonds broken by looking at sheet
- Calculate Bonds made
- Find the difference
- Draw graph
The trend in the Burning Alcohol experiment?
The greater the Mr of the alcohol the more energy was transformed per gram of fuel.
To make new chemicals we need to….
Break bonds.
When we make new substances we need to break bonds and …..
Make new ones.
What is bond energy?
The energy that is needed to break chemical bonds.
The units for ΔH?
kJmol-1
Thermo Chemistry Enthalpy questions EXAMPLES?
LOOK IN BOOK
Method for Calorimeter burning fuels?
- Set up apparatus
- Weigh spirit burner
- Light burner and wait until the water temperature has risen by 15-20oC - Then put out the burner.
- Repeat with other alcohols
General Symbol equation for a Alcohol?
CnH2n+1OH
General Symbol equation for an Alkane?
CnH2n+2
General Symbol equation for an Alkene?
CnH2n
Equation for moles?
moles = mass / Mr
Equation for Mass?
mass = Mr x moles
Energy transferred to water =
mass x specific heat capacity x temp change
If the ΔH goes down?
The answer is negative and exothermic.
If the ΔH goes up?
The answer is positive and endothermic.
What is thermal decomposition?
Mostly used for making CO2 in the lab by heating metal carbonates.
Equation for thermal decomposition?
Metal carbonate -Heat-> Metal Oxide + CO2
Thermal decomposition of Magnesium Carbonate?
MgCO3 -> MgO + CO2
