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Sub-Topic 3.1

Using & Controlling Reactions: Measuring Energy Changes

QuestionAnswer
What is enthalpy? The heat released or absorbed in a reaction at constant pressure.
What is the enthalpy value? ΔH = ∑H products - ∑H reactants
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
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.
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.
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.
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.
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.
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.
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.
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)
What is the formula for enthalpy? ΔH = 4.18 x ΔT x V/1000 x n
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.
What is an exothermic reaction in nature? Respiration
What is an endothermic reaction in nature? Photosynthesis
Created by: MahaliaMcD