Measuring Enthalpy Changes

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  • Created by: Lotto65
  • Created on: 26-02-17 19:39
Give a definition of energy
The ability to do work (move a force through a distance)
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What is the unit of energy?
Joules
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Energy =
Force x Distance
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What is given out when bonds are made?
Energy
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What is required to break bonds?
Energy
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What is the most important type of energy in chemistry?
Heat
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In an exothermic reaction, are the bonds in the reactants or products stronger?
Products
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What is the principle of exothermic reactions?
Heat is given out to the surroundings
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Give two examples of exothermic processes
Combustion and neutralisation
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In an endothermic reaction, are the bonds in the reactants or products stronger?
Reactants
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What does it mean if the bonds in the reactants are stronger than the products?
Heat is absorbed from the surroundings
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What is enthalpy?
The internal energy stored in reactants
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Can we ever know the absolute value of an enthalpy or the enthalpy of the products?
No
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What can we measure in terms of enthalpy?
The difference in enthalpy between the reactants and products
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What value does an enthalpy have if it is an endothermic reaction?
Positive
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What value does an enthalpy have if it is an exothermic reaction?
Negative
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What sort of conditions are enthalpy changes given in?
Standard conditions
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What defines a standard condition?
100kPa pressure and 298K temperature
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In an endothermic reaction, are the reactants or products more stable?
Reactants
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In an exothermic reaction, are the reactants or products more stable?
Products
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What is heat?
The total amount of energy in a certain amount of substance
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What does heat depend on?
The amount of substance present
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What is temperature?
A measure of the 'hotness' of a substance. The measure of the average kinetic energy present in a substance
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Does temperature rely on the amount of substance present?
No
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What piece of equipment can measure enthalpy change experimentally?
Calorimeter
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The heat produced in a calorimeter in an exothermic reaction is used to do what?
Raise the temperature of the water (known mass)
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How can we calculate the heat transferred from the water to the reaction in a calorimeter?
Measure the lowering of temperature
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Why do we need to extrapolate temperature - time graphs for calorimeter experiments?
Some heat would have been lost to the surroundings so the results are not accurate. We can see the temperature rise if the reaction was instantaneous.
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Give two ways you can prevent heat loss to the surroundings with a calorimeter?
Use an insulating material to contain the reaction mixture (polystyrene cup); Put a lid over the reaction mixture to prevent heat escaping upwards
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Other cards in this set

Card 2

Front

What is the unit of energy?

Back

Joules

Card 3

Front

Energy =

Back

Preview of the front of card 3

Card 4

Front

What is given out when bonds are made?

Back

Preview of the front of card 4

Card 5

Front

What is required to break bonds?

Back

Preview of the front of card 5
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