Chemistry Revision A

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What is the definition of Enthalpy of combusion?
The Enthalpy change when one mole of a compound is burned completely in oxygen under standard conditions of 100kPa and 298K and with everything in its standard states
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What is meant by Bond Enthalpy?
The minimum amount of energy needed to break a bond
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An exothermic reaction produces which Enthalpy change, positive or negative?
Negative Enthalpy change for exothermic reactions
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What is the equation for calculating Enthalpy change?
Enthalpy change of reaction=Total energy absorbed-Total Energy released
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How do you work out Enthalpy change from the equation q=mc(delta)t?
First, work out q and the divide q by the number of moles and this will give you the Enthalpy change.
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State Hess's Law?
The total Enthalpy change of a reaction is independent of the route taken. Hess's law shows that the Enthalpy change for route 1 is equal to the Enthalpy change for alternative routes.
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What are the different types of Enthalpy change?
1. Standard Enthalpy change of formation 2. Standard Enthalpy change of combustion 3. Standard Enthalpy change of reaction
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What is a Redox reaction?
A reaction where oxidation and reduction happen simultaneously
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What is Oxidation?
Oxidation is the loss of electrons
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What is Reduction?
Reduction is the gain of electrons
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What does the oxidation state of an element tell you?
The number of electrons that have been lost or gained
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What is the oxidation number of a stand alone element in a reaction?
A stand has a 0 oxidation number
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Why are electrons shown in half equations?
So that the charges in the equations balance
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Why is High Resolution Mass Spectrometry used instead of normal Mass Spectrometry?
High Resolution Mass Spectrometry produces a highly accurate measurement which can differentiate between compounds that would appear the have the same Molecular mass if they were rounded to the nearest whole number
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What does the Molecular Ion Peak on the spectrum represent?
The Molecular Ion Peak represents the Molecular mass (Mr) of a compound
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How does Infrared Spectroscopy happen?
A beam of IR radiation is passed through a sample of a chemical. the IR is absorbed by the covelant bonds in the molecules, increasing their vibration energy. Bonds between different atoms absorb different frequencies of IR.
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What is the fingerprint region?
The fingerprint region is a region on the IR spectroscopy graph that is unique to the compound you are testing which means you are able to find out what compound it is.
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What properties does a reaction in equilibrium have to have
Forward and backward reaction both occur at the same rate. The ratio of products to reactants has to remain constant throughout the reaction.
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What is Le Chatelier's principle?
If a reaction at equilibrium is subjected to a change in temperature, pressure or concention, then the position of equilibrium will move to counteract that change.
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What affect does changing the pressure have on the position of equilibrium?
Increasing the pressure shifts the position of equilibrium to the side with fewer gas molecules. This the reduces the pressure causing it to shift back which causes the pressure to increase etc.
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What affect does changing the temperature have on the position equilibrium?
Increasing the temperature causes the equilibrium the shift in the endothermic direction to absorb the temperature. Decreasing the temperature causes a shift in the exothermic direction.
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What is the Equilibrium constant?
The Equilibrium constant (Kc) is a ratio worked out from the concentrations of the products and reactants after equilibrium is reached.
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What is the formula layout of the Kc equation?
Kc=
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How does changing temperature affect Kc?
Increasing the temperature will cause a shift in the endothermic direction so dependent on whether your reaction is endothermic or exothermic will decide with Kc increases or decreases
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How does changing concentration affect the equilibrium constant?
Kc is fixed at a given temperature so if the concentration of one compound changes then so will the others which means that the equilibrium constant won't be affected by changing the concentration
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What affect does adding a catalyst have on the value of Kc?
Adding a catalyst doesn't affect the value of Kc as it increases the rate of both the forward and backward reaction by the same amount
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What is a catalyst?
A catalyst provides an alternative reaction pathway of reduced activation energy which means a reaction can happen at a quicker rate
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What does collision theory state?
A reaction between two particles will only take place if they collide in the right direction and with a minimum amount of kinetic energy to cause a successful collision
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What is the Equation for rate of reaction?
Rate of Reaction=
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What is meant by Bond Enthalpy?

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The minimum amount of energy needed to break a bond

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An exothermic reaction produces which Enthalpy change, positive or negative?

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Card 4

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What is the equation for calculating Enthalpy change?

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How do you work out Enthalpy change from the equation q=mc(delta)t?

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