# AS Calculations and Enthalpy

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• Created by: leenaq
• Created on: 08-04-14 18:26
What is a mole?
The amount of substance that has as many single particles as there are atoms in exactly 12g of a carbon-12 isotope
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What is the definition of relative atomic mass?
The average mass of an atom of an element compared with one-twelfth the mass of an atom of carbon-12
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What is the definition of relative isotopic mass?
The mass of an elements' isotope on a scale where an atom of carbon-12 is 12
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What is the definition of relative molecular mass?
The average mass of a compounds' molecule compared with one-twelfth the mass of an atom of carbon-12
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What is the equation for the number of moles (using particles)?
No. of particles you have / No. of particles in a mole
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What is the equation for the number of moles (using mass)?
mass of substance(s) / molar mass
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What is the equation for the number of moles in concentration?
concetration x volume (cm3) / 1000 or concentration x volume (dm3)
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What is the equation for the number of moles in gas volume?
volume in dm3/ 24 or volume in cm3/ 24000
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Enthalpy change (∆H) is...
The heat energy transferred in a reaction at constant pressure
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Do exothermic reactions release or absorb energy?
Releases energy, the ∆H is negative
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Do endothermic reactions release or absorb energy?
Absorbs energy, the ∆H is positive
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What is the activation energy?
The minimum amount of energy needed to begin breaking reactant bonds and start a chemical reaction
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Enthalpy change is affected by two things which are?
Temperature and pressure
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What are the standard conditions?
Pressure of 100kPa, Temperature of 298K or (25C), Concentration of 1 mol dm-3, Standard state the physical state of the substance in the standard temperature
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What is the definition of the standard enthalpy change of reaction?
the enthalpy change when the reaction occurs in molar quantities represented in a chemical equation
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What is the definition of the standard enthalpy change of formation?
The enthalpy change when 1 mole of a compound is formed from its elements
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What is the definition of the standard enthalpy change of combustion?
The enthalpy change when 1 mole of a substance is completely burned in oxygen
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What is the definition of the standard enthalpy change of neutralisation?
The enthalpy change when 1 mole of water is formed from the neutralisation reaction of hydrogen and hydroxide
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What is the definition of the standard enthalpy change of reaction?
The enthalpy change when 1 mole of an element is converted to gaseous atoms
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Hess's Law states that...
The total enthalpy change of a reaction is always the same, no matter which route is taken
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## Other cards in this set

### Card 2

#### Front

What is the definition of relative atomic mass?

#### Back

The average mass of an atom of an element compared with one-twelfth the mass of an atom of carbon-12

### Card 3

#### Front

What is the definition of relative isotopic mass?

### Card 4

#### Front

What is the definition of relative molecular mass?

### Card 5

#### Front

What is the equation for the number of moles (using particles)?