Unit 1 Section 4: Energetics

?
What is enthalpy change?
It is the heat energy transferred in a reaction at constant pressure
1 of 29
What are standard conditions?
100kPa and 298K (25 degrees)
2 of 29
What are exothermic reactions?
Bond breaking
3 of 29
What are endothermic reactions?
Bond making
4 of 29
Do the products or reactants have more energy in an exothermic reaction?
The reactants have more energy
5 of 29
What is the enthalpy change in exothermic reactions?
Negative
6 of 29
What is the enthalpy change in endothermic reactions?
Positive
7 of 29
What are the units of enthalpy change?
kj mol-1
8 of 29
What is an example of an exothermic reaction?
Combustion, (oxidation reactions)
9 of 29
Do the products or reactants have more energy in an endothermic reaction?
The products have more energy
10 of 29
Name an endothermic reaction
Photosynthesis
11 of 29
What are the differences between endothermic and exothermic reactions?
Exo give out energy, endo absorb energy. In exo reactions the enthalpy change is negative, in endo it is positive.
12 of 29
Define bond enthalpy
The energy needed to break a bond
13 of 29
What is mean bond enthalpy?
The average energy needed to break a certain type of bond, over a range of compounds
14 of 29
How do you work out the overall enthalpy change of a reaction?
Total energy absorbed - total energy released
15 of 29
Define standard enthalpy change of formation
It is the enthalpy change when 1 mole of a compound is formed from its elements in their standard states under standard conditions
16 of 29
Define standard enthalpy change of combustion
It is the enthalpy change when 1 mole of a substance is completely burned in oxygen under standard conditions with all reactants and products in their natural states
17 of 29
Define standard enthalpy change of reaction
It is the enthalpy change when a reaction occurs in the molar quantities shown in the chemical equation, under standard conditions with all reactants and products in their standard states
18 of 29
What experiments measure the heat given out by certain reactions?
Calorimetry experiments
19 of 29
How do you find the enthalpy change of combustion of a flammable liquid?
You burn it inside a calorimeter
20 of 29
What is the equation for enthalpy change?
Mass X specific heat capacity X change in temperature
21 of 29
What is q in q=mc∆T?
Heat lost/gained in joules (this is the same as enthalpy change if the pressure is constant)
22 of 29
How do you calculate the standard enthalpy change of combustion?
Calculate heat lost/gained in q=mc∆T and change the units of q to kilojoules, then calculate the number of moles of fuel that caused the enthalpy change, then divide q (kj) by number of moles
23 of 29
What is the final equation used to calculate the standard enthalpy change of combustion?
Actual heat change / number of moles
24 of 29
What is the enthalpy change of neutralisation?
It is the energy change when one mole of water is formed by the reaction of an acid and an alkali
25 of 29
How do you find the enthalpy change for a neutralisation reaction?
You add a known volume of acid to an insulated cup and measure the temperature, then add a known volume of alkali and record temperature rise. Stir to distribute heat evenly.
26 of 29
What are two problems with calorimetry?
Some heat will be absorbed by the container, instead of the water & some heat is always lost to surroundings
27 of 29
What are 2 problems with calorimetry that only apply to flammable liquid calorimetry?
Some combustion may be incomplete (meaning less energy will be given out) & some of the flammable liquid may escape by evaporation (they're usually volatile)
28 of 29
What is hess's law?
The total enthalpy change for a reaction is independence of the route taken
29 of 29

Other cards in this set

Card 2

Front

What are standard conditions?

Back

100kPa and 298K (25 degrees)

Card 3

Front

What are exothermic reactions?

Back

Preview of the front of card 3

Card 4

Front

What are endothermic reactions?

Back

Preview of the front of card 4

Card 5

Front

Do the products or reactants have more energy in an exothermic reaction?

Back

Preview of the front of card 5
View more cards

Comments

No comments have yet been made

Similar Chemistry resources:

Unit 2
See all Chemistry resources »See all Energetics resources »