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Flashcards in 4 energetics Deck (18):
1

thermochemistry

the study of heat changes during chemical reactions

2

exothermic

describes a reaction in which heat is given out as the reactants change to products; the temp thus rises

3

endothermic

describes a reaction in which heat is taken in as the reactants change to products; the temp thus drops

4

enthalpy change

a measure of the heat energy change given out or taken in when a chemical or physical change occurs at constant pressure
q=mc[delta]T

5

standard conditions

100kPa and a stated temp (298K)

6

standard molar enthalpy of formation

the enthalpy change when 1 mole of a substance is formed from its constituent elements under standard conditions, with all reactants and products in their standard states (298K and 100kPa)

7

standard molar enthalpy of combustion

the enthalpy change when 1 mole of a substance is completely burnt in oxygen under standard conditions, with all reactants and products in their standard states (298K and 100kPa)

8

temperature

the average kinetic energy of the particles in a system

9

heat

the total energy of all particles present in a given amount of substance

10

specific heat capacity

the amount of heat needed to raise the temp of 1g of substance by 1K

11

calorimeter

an instrument for measuring the heat changes that accompany chemical reactions

12

Hess's law

"the enthalpy change for a chemical reaction is independent of the route taken from reactants to products"

13

thermochemical cycle

a sequence of chemical reactions (with their enthalpy changes) that convert a reactant into a product). the total enthalpy change of the sequence of reactions will be the same as that for the conversion of the reactant to the product directly (or by any other route)

14

enthalpy diagrams

diagrams in which the enthalpies (energies) of the reactants and products of a chemical reaction are plotted on a vertical scale to show their relative levels

15

enthalpies of all elements in their standard states

0 (the states at which they exist at 298K and 100kPa - normal room conditions)

16

allotropes

pure elements which can exist in different physical forms in which their atoms are arranged differently e.g. diamond, graphite, buckminsterfullerene - allotropes of carbon

17

bond dissociation enthalpy

the enthalpy change required to break a covalent bond with all species in the gaseous state

18

mean bond enthalpy

the average value of the bond dissociation enthalpy for a given type of bond taken from a range of different compounds