C9- Enthalpy Flashcards

1
Q

What is enthalpy

A

a measure of heat energy in a chemical system

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2
Q

What is a chemical system

A

atoms, molecules or ions making up the chemicals

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3
Q

exothermic reaction

A

Energy is transferred from the chemical system to the surroundings

results in a temperature increase

negative enthalpy change

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4
Q

Endothermic reaction

A

energy is transferred from the surroundings to the chemical system

Results in a temperature decrease

positive enthalpy change

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5
Q

What is activation energy

A

minimum energy required for a reaction to take place

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6
Q

Standard conditions

Pressure, temperature, concentration

A

Pressure= 100kPa

Temperature= 25c or 298K

concentration= 1M

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7
Q

Standard enthalpy change of reaction

define

A

enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation under standard conditions, with all reactants and products in their standard states

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8
Q

Standard enthalpy change of formation

Define

A

Enthalpy change that takes place, when one mole of a compound is formed from its elements under standard conditions with all reactants and products in their standard states

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9
Q

Standards enthalpy change of formation of an element

value

A

always zero

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10
Q

standard enthalpy change of combustion

define

A

Enthalpy change that takes places when one mole of a substance reacts completely with oxygen under standard conditions with all reactions and products in their standard states

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11
Q

Standard enthalpy change of neutralisation

A

energy change that accompanies reaction of an acid by a base to form one mole of water under standard conditions and all reactants and products in their standard states

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12
Q

Specific heat capacity

define

A

The energy required to raise the temperature of 1g of a substance by 1K

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13
Q

How to experimentally determine the enthalpy change of combustion of a fuel

A

beaker of water of known mass over a spirit burner

weigh spirit burner before and after usage

heat water by 15c

measure change in mass of spirit burner

use formula q=mcT

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14
Q

Heat energy change formula

A

q= m c T

Mass

specific heat capacity Jgk

Change in temperature c or K

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15
Q

Problems with accuracy of experimental determination of enthalpy change of combustion

A

heat lost to surroundings other than water

incomplete combustion, forms soot on bas of beaker

evaporation of fuel from wick (place cap on right after extinguishing)

Non standard conditions

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16
Q

Impact of problems with accuracy of experimental determination of enthalpy change of combustion

A

leads to the enthalpy change being less exothermic than was expected

17
Q

How to experimentally determine enthalpy change of reaction

A

solid added to solution in a polystyrene cup

Take temperature readings every 30 seconds

Plot values on graph

18
Q

How to find maximum temperature on a time/temperature graph

A

Extrapolate from each section of graph, intersection of lines is the max temp

19
Q

How to determine enthalpy change of neutralisation experimentally

A

In a polystyrene cup add two solutions

record temperature every 30 seconds

plot values on a graph

20
Q

Enthalpy change units