Hess' Law Definitions

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Flashcards by jessnrm98, updated more than 1 year ago
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Fundamental definitions when learning about Hess' Law.
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Question Answer
What is the Enthalpy Change of a Reaction? The enthalpy change when the amount of reactants shown in the equation react under standard conditions to give the products in their standard states.
What is the Enthalpy Change of Combustion? The enthalpy change when one mole of the substance is burnt in excess oxygen under their standard conditions.
What is the Enthalpy Change of Formation? The enthalpy change when one mole of a substance is formed form its elements in their standard states.
Define exothermic. Put simply; this is when heat is released into the surroundings. Enthalpy of the products is significantly lower than the enthalpy of its reactants - therefore showing a negative value to indicate a decrease in enthalpy (from reactants to products). Exothermic reactions also release energy to form bonds.
Define endothermic. Put simply; this is when heat is taken in from its surroundings. Enthalpy of the products is significantly higher than its reactants - therefore showing a positive value to indicate the increase in enthalpy (from reactants to products). Endothermic reactions also take in energy to break bonds.
State Hess' Law. The enthalpy change of a reaction depends on the initial and final states of a reaction - independent of the route by which it occurs.
State the term enthalpy. The heat content / energy stored in a chemical system.
State the standard conditions. The conditions required for all enthalpy calculations to occur - in which substances must also be in their standard states / most stable physical states.
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