enthalpy change

Question 1

what is H

Answer 1

enthalpy, measure of the het energy in a chemical system

Question 2

what is the chemical system?

Answer 2

refers to the atoms molecules , or ions making up the chemicals.

Question 3

enthalpy change?

Answer 3

= H(products)- H(reactants)

change in H can be negative or positive dependin on whether the products contain more or less energy than the reactants.

Question 4

law of conservation of energy ?

Answer 4

states that energy cannot be created or destroyed

Question 5

. what is the system in. chemical reaction involving enthalpy changes?

Answer 5

system- the chemicals - the reactants and the products

Question 6

whats the surroundings in a chem reaction involving enthalpy changes?

Answer 6

surroudnings- the apparatus, the laboratory and evrything thats not the chem system

Question 7

exothermic reaction

Answer 7

energy transferred from the system to the surroundings

Question 8

endothermic reaction

Answer 8

energy transferred from surroundings to the system

Question 9

activation energy

Answer 9

minimum energy required for a reaction to take place

Question 10

units for standard enthalpy change?

Answer 10

KJmol^-1

Question 11

standard pressure?

Answer 11

100 kpa

Question 12

standard temp ?

Answer 12

298K (25 dc)

Question 13

standard concentration?

Answer 13

1mol dm^-3

Question 14

standard state?

Answer 14

the physical state of a substance under standard conditions - 100 kPa and 298K

Question 15

standard enthalpy change of reaction?

Answer 15

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

Question 16

standard enthalpy change of formation ?

Answer 16

the 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.

Question 17

enthalpy change of combustion ?

Answer 17

enthalpy chnge that takes place when one mol of a substance reacts completely with oxygen under standard conditions, with all reactants and products in their stand. states.

Question 18

enthalpy change of neutralisation

Answer 18

energy change that accompanies the reaction of an acid by a base to form one mole of H2O (l) udner stand. cond. with all reactants and products in their standard states.

Question 19

0 kelvins in degrees cels.

Answer 19

-273 degrees

Question 20

why is a 1k rise in temp the same as 1 degrees rise in temp ?

Answer 20

if use a thermometer graduated in degrees celsius the value of temp change is exacly the same in degrees and K

Question 21

specific heat capacity (c)

Answer 21

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

Question 22

what is the c of water

Answer 22

4.18Jg^-1K^-1

Question 23

equation for calculating (heat energy change (q))?

Answer 23

mass x c x change in temp

Question 24

why may less heat be transferred to water in na experiment that tests the enthalpy change of combustion of methanol ?

Answer 24

heat loss to surroundings otehr than water
incomplete comb. of methanol
evaporation of methanol from the wick
non-standard conditions