2.2 Energetics

HideShow resource information
• Created by: Danielle
• Created on: 05-01-14 13:44
What is enthalpy?
The heat content of a system
1 of 23
What is the symbol for enthalpy?
H
2 of 23
What is enthalpy change?
The heat added to a system at constant pressure
3 of 23
What is the symbol of enthalpy change
triangleH
4 of 23
What is the standard enthalpy change of formation?
The enthalpy change when one mole of a substance is formed from its constituent elements in their standard states under standard conditions
5 of 23
What is the symbol for standard enthalpy change of formation
..
6 of 23
What is the symbol for standard enthalpy change of combustion
..
7 of 23
What is the standard enthalpy change of combustion
The enthalpy change when one mole of a substance is completely combusted in oxygen under standard conditions
8 of 23
What are standard conditions?
298 k / 25 degrees c 7 1 atm / 101 kPa
9 of 23
What is the equation from enthalpy change?
enthaply change = H products - H reactants
10 of 23
If the enthalpy change value is negative, is the reaction endothermic or exothermic?
Exothermic
11 of 23
If the enthalpy change value is positive, is the reaction endothermic or exothermic?
Endothermic
12 of 23
Why does H2 have a standard enthalpy change of formation of 0 kJ mol-1?
Because its elements are already in their standard state
13 of 23
What is Hess's Law?
States that the total enthalpy change for a reaction is independent of the route taken from the reactants to the produts
14 of 23
What is the equation for Hess's Law?
Enthalpy change 1 = enthaply change 2 + enthalpy change 3
15 of 23
What is different about a enthalpy cycle using enthalpy change of combustion?
The direction of the arrows (goes from reactants and products to the common combustion products)
16 of 23
What is different about a enthalpy cycle using enthalpy change of formation?
The direction of the arrows (goes from common elements to the reactants and products)
17 of 23
What is specific heat capacity (c)?
The energy required to raise the temperature of 1 g of a substance by 1 K
18 of 23
What is the equation for calculation of enthalpy change and what does each symbol stand for?
..
19 of 23
What are the two main sources of error in the experimental determination of enthalphy change of combustion?
- Heat loss to surroundings - Incomplete combustion of the fuel
20 of 23
*6 The combustion of 1.50 g of ethanol raised the temp of 500 cm3 of water by 19.5 degrees c. Calculate the molar enthalpy change of combustion of ethanol C2H5OH (c=4.18JgK-1)
-1250 kJ
21 of 23
What is average bond enthalpy?
The average value of the enthalpy required to break a given type of covalent bond in the molecules of a gaseous species
22 of 23
What is bond enthalpy?
The enthalpy required to break a covalent X-Y bond into X and Y atoms, all in the gas phase
23 of 23

Other cards in this set

Card 2

Front

What is the symbol for enthalpy?

H

Card 3

Front

What is enthalpy change?

Card 4

Front

What is the symbol of enthalpy change

Card 5

Front

What is the standard enthalpy change of formation?