# Enthalpy

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• Created by: Voltace
• Created on: 26-05-14 13:01
What is endo & exothermic? and what is making and breaking??
Endo takes in energy, exothermic gives out energy (Exo = Delta H -) & (Endo = Delta H +) Making = Exo Breaking = Endo
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What is bond enthalpy & what is mean bond enthalpy?
Energy to make & break, energy required to break individual bond, can vary where it is
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What is the formula for working out enthalpy change?
Total energy absorbed - Energy Released = Enthalpy change
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What does the sub-way symbol, mean? and what does Deltha H mean? and what are the standard conditions?
Standard States & Conditions, Delta H = Heat transferred at constant pressure. Standard conditions = 100Kpa & Stated Temp
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Definition of Enthalpy change of reaction?
Enthalpy change when a reaction occurs in the molar quantities shown in the chemical equation, under standard conditions and reactants & products in standard states.
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Definition of Enthalpy change of combustion?
Enthalpy change when one mole of a substance is completly burned in oxygen under standard conditions with reactants and products in their standard states
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Defin ition of Enthalpy change of formation?
enthalpy change when one mole of a compound is formed from it's elements in their standard states under standard conditions.
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How do you work out changes in lab?
No. of Moles & Change in Tempreature -> Some reactions take place in polycup & thermometer -> Combustion = calorimeter with known mass of water &record temp change - > Bomb Calorimeter = More accurate
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How do you work out the heat loss or gained? What do symbols stand for?
q=mc△T q= heat loss or gained , m = mass in grams c= heat capacity 4.18 , △T = tempreature change
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Why is the measured change different to one in data book?
Heat can be lost or gained in surrounding & incomplete combustion
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How to work out enthalpy change of a reaction?
1. q=mc△T 2. J to KJ ( ÷1000 ) 3. Moles of one reactant 4. Calculate q ÷ n x no. of moles reacting in balanced eq.
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How to work out enthalpy change of combustion?
1. q=mc△T 2. J to KJ ( ÷ 1000 ) 3. No. of moles of fuel that caused enthalpy change (from mass of reactants) 4. q ÷ n = standard enthalpy
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What is Hess's law?
The enthalpy change of a reaction is always the same no matter which route is taken ( Route one = Route Two )
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What are the general rules to follow for combustion, formation , reaction in working out Enthapy change in routes?
Formation: Elements = 0 Reaction: Groups of linked reactions Opposite arrows + become - & reverse
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## Other cards in this set

### Card 2

#### Front

What is bond enthalpy & what is mean bond enthalpy?

#### Back

Energy to make & break, energy required to break individual bond, can vary where it is

### Card 3

#### Front

What is the formula for working out enthalpy change?

### Card 4

#### Front

What does the sub-way symbol, mean? and what does Deltha H mean? and what are the standard conditions?

### Card 5

#### Front

Definition of Enthalpy change of reaction?

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