Thermochemistry

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  • Created by: zoolouise
  • Created on: 02-06-16 08:35
What is an exothermic reaction?
It releases energy to the surroundings, there's a temperature rise and the ΔH is negative
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What is an endothermic reaction?
It takes in energy from the surroundings, there's a temperature drop and ΔH is positive
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What are some examples of exothermic reactions?
Acids with metals, In hand warmers (oxidation of iron), Thermite reaction (aluminium and iron(III) oxide)
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What are some examples of endothermic reactions?
Melting ice, In cold packs, Thermal decomposition of group 2 carbonates
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What is the definition of enthalpy?
Ethalpy, H, is the heat content of a system at a constant pressure
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What's the definition of enthalpy change?
Enthalpy change, ΔH, is the heat added to a system at a constant temperature
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How do you measure enthalpy change?
ΔH = Hproducts - Hreactants
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How do you measure enthalpy for exothermic reactions?
ΔH = Hproducts - Hreactants ΔH is negative
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How do you measure enthalpy for endothermic reactions?
ΔH = Hreactants - Hproducts ΔH is positive
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What is the principle of conservation of energy?
The principle of conservation of energy states that energy can't be created or destroyed only changed from one form to another
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What are the fixed conditions of standard enthalpy change?
All substances must be in their standard states. A temperature of 298K (25 degrees celcius). A press of 1atm (10
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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 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 is Hess's Law?
Hess's Law states that the total enthalpy change for a reaction is independent of the route taken from the reactants to the products.
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What's the calculation for Hess's Law?
ΔH1 = ΔH2 + ΔH3 Route 1 = Route 2
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What is the definition of bond enthalpy?
Bond enthalpy is the enthalpy required to break a covalent X-Y bond into X atoms and Y atoms, all in the gas phase.
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What is the definition of average bond enthalpy?
Average bond enthalpy is 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's the value of bond enthalpies?
Always positive because breaking a bond requires energy
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How do you calculate bond enthalpies?
1) Draw out each molecule to show bonds. 2) Calculate energy required to break bonds in the reactants (+) 3) Calculate energy released in forming bonds in products (-) 4) Add together the enthalpy changes
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How do you measure the heat transferred to the surroundings?
Carry out a chemical change in an insulated container called a calorimeter. Measure the enthalpy change of reaction with a thermomemeter.
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What is the specific heat capacity?
Specific heat capacity is the heat required to raise the temperature of 1g of a substance by 1K. The value for water is 4.18Jg-1k-1
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What is the calculation for heat transferred?
q = mcΔT
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What do the letters/symbols stand for?
q = heat transferred, m = mass, c = specific heat capacity (4.18), ΔT = temperature change
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Card 2

Front

What is an endothermic reaction?

Back

It takes in energy from the surroundings, there's a temperature drop and ΔH is positive

Card 3

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What are some examples of exothermic reactions?

Back

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Card 4

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What are some examples of endothermic reactions?

Back

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Card 5

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What is the definition of enthalpy?

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