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Flashcards in Enthaply Deck (14):
1

Endothermic

- the energy required to break old bonds is greater than the energy released when you bonds are formed
- energy is taken in

2

Exothermic

- The energy released in bond formation is greater than the energy used in breaking bonds
- energy is given out

3

What is the change in energy called

Enthalpy change, unit kJ/mol

4

Enthalpy change value is negative when it is a...

Exothermic reaction

5

I want to be changes positive when it is a…

Endothermic reaction

6

What is activation energy

The minimum energy needed by reacting particles for the reaction to occur

7

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

8

What can we use to measure the amount of energy transferred in a chemical reaction

Calorimetry

9

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

10

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

11

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

12

Equation to calculate the heat energy transferred

= 4.2 x mass of water x temperature change

13

Equation to calculate energy per gram of a spirt

= energy produced ÷ mass of fuel used

14

Calculating energy per mole of a spirt (molar enthalpy change)

- calculate amount of energy transferred
- calculate moles
- energy transferred divided by mole