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Using & Controlling Reactions: Measuring Energy Changes

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Question
Answer
What is enthalpy?   The heat released or absorbed in a reaction at constant pressure.  
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What is the enthalpy value?   ΔH = ∑H products - ∑H reactants  
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What are the certain standard conditions for determining enthalpy?   1) Set temperature of 25°C 2) 1 mol of substance involved 3) Constant pressure of one atmosphere 4) Heat is measured in kJ 5) Solutions are 1M  
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What is an exothermic reaction?   A reaction wherein energy is released. The enthalpy value is negative and there is a temperature rise in the surroundings.  
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What is an endothermic reaction?   A reaction wherein energy is absorbed. The enthalpy value is positive and there is a temperature decrease in the surroundings.  
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What is the standard enthalpy of reaction? ΔH°   The heat evolved or absorbed when the molar quantity of the reactants have completely reacted under standard conditions.  
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What is the standard enthalpy of formation? ΔH°f   The heat evolved or absorbed when 1 mole of a compound is formed from its constituent elements under standard conditions.  
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What is the standard enthalpy of combustion? ΔH°c   The change when 1 mole of substance is completely burnt in excess oxygen under standard conditions.  
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What is the standard enthalpy of neutralisation? ΔH°neut   The heat evolved when 1 mole of hydrated hydrogen ions (H+)from an acid is neutralised by 1 mole of hydrated hydroxide ions (OH-) from an alkali. The ΔH°neut is always -57kJ.  
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What is the standard enthalpy of solution? ΔH°sol   The heat evolved or absorbed when 1 mole of solute is dissolved in sufficient solvent so that further dilution causes no further temperature change.  
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What is the formula for energy/heat released?   Energy/heat released = 4.18 x ΔT x V *Where ΔT is the initial - final temperature, V is the volume in mL and the energy/heat is given in joules (J)  
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What is the formula for enthalpy?   ΔH = 4.18 x ΔT x V/1000 x n  
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What assumptions are made in calculating the enthalpy value?   1) it takes 4.18J to raise 1.0g of water to 1°C (specific heat capacity of water). 2) The density of water is 1g/mL 3) No is heat is lost or gained from the surroundings. 4) Any solution has the same heat capacity and density as water.  
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What is an exothermic reaction in nature?   Respiration  
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What is an endothermic reaction in nature?   Photosynthesis  
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