Enthaply Flashcards
Endothermic
- the energy required to break old bonds is greater than the energy released when you bonds are formed
- energy is taken in
Exothermic
- The energy released in bond formation is greater than the energy used in breaking bonds
- energy is given out
What is the change in energy called
Enthalpy change, unit kJ/mol
Enthalpy change value is negative when it is a…
Exothermic reaction
I want to be changes positive when it is a…
Endothermic reaction
What is activation energy
The minimum energy needed by reacting particles for the reaction to occur
How do you calculate and to be changed for a reaction
- add up the energy of the bonds that are broken
- Subtract the energy of the bonds that are made
What can we use to measure the amount of energy transferred in a chemical reaction
Calorimetry
How can we use calorimetry to measure enthalpy change
- measure the temperature of the reagents (make sure they are all the same temperature)
- mix them
- measure the temperature of the solution at the end of the reaction
OR!!!
Spirit burner method
What should use use to make sure your results are accurate when using a calorimetry
- polystyrene cup and cotton wall filled beaker to insulate it
- a lid on the cup to stop energy loss from evaporation
Spirt burner calorimetry method
- use a screen to reduce drafts
- put 50cm3 of water into a copper beaker + measure its temp
- weigh the spirt burner and lid
- put the SB under the beaker and light it
- heat the water to around 50c
- put out the flame using the lid
- measure final temp of water
- weigh SB and lid again
- use measurements to calculate E Change
Equation to calculate the heat energy transferred
= 4.2 x mass of water x temperature change
Equation to calculate energy per gram of a spirt
= energy produced ÷ mass of fuel used
Calculating energy per mole of a spirt (molar enthalpy change)
- calculate amount of energy transferred
- calculate moles
- energy transferred divided by mole
