2.2 Energetics

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  • Created by: Danielle
  • Created on: 05-01-14 13:44
What is enthalpy?
The heat content of a system
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What is the symbol for enthalpy?
H
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What is enthalpy change?
The heat added to a system at constant pressure
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What is the symbol of enthalpy change
triangleH
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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
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What is the symbol for standard enthalpy change of formation
..
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What is the symbol for standard enthalpy change of combustion
..
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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
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What are standard conditions?
298 k / 25 degrees c 7 1 atm / 101 kPa
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What is the equation from enthalpy change?
enthaply change = H products - H reactants
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If the enthalpy change value is negative, is the reaction endothermic or exothermic?
Exothermic
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If the enthalpy change value is positive, is the reaction endothermic or exothermic?
Endothermic
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Why does H2 have a standard enthalpy change of formation of 0 kJ mol-1?
Because its elements are already in their standard state
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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
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What is the equation for Hess's Law?
Enthalpy change 1 = enthaply change 2 + enthalpy change 3
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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)
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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)
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What is specific heat capacity (c)?
The energy required to raise the temperature of 1 g of a substance by 1 K
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What is the equation for calculation of enthalpy change and what does each symbol stand for?
..
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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
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*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
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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
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What is bond enthalpy?
The enthalpy required to break a covalent X-Y bond into X and Y atoms, all in the gas phase
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What is the symbol for enthalpy?

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H

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What is enthalpy change?

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What is the symbol of enthalpy change

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What is the standard enthalpy change of formation?

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