4- energetics

Question 1

what do most chemical reaction do

Answer 1

give out or take in energy as they proceed

Question 2

why is the energy involved in chemical reactions important

Answer 2

• you can measure the energy values of fuels
• you can caluclate the energy requirements for industral processes
• you can work out th etheoretical amount of energy to break bonds and the amount of energy released when bonds are made
• helps predict whether or not a reaction will take place

Question 3

thermochemistry

Answer 3

the study of heat changes during a chemical reaction

Question 4

what happens when a chemical reaction takes place

Answer 4

chemical bonds break and new ones are formed

Question 5

breaking bonds

Answer 5

energy must be put in

Question 6

forming bonds

Answer 6

energy is given out

Question 7

exothermic

Answer 7

energy is given out

Question 8

endothermic

Answer 8

energy is taken in

Question 9

exothermic reaction

Answer 9

gives out heat as it proceedse

Question 10

example of exothermic reaction

Answer 10

neutralising an acid with an alkali

Question 11

endothermic reaction

Answer 11

takes in heat from their surroundings to keep the reaction going

Question 12

endothermic reaction example

Answer 12

the breakdown of limestone to line and carbon dioxide

Question 13

what does the amount of heat given out or taken in during a reaction depend on

Answer 13

• temperature
• pressure
• concentration of solutions

Question 14

how is energy measured

Answer 14

KJmol-1

Question 15

what happens when fuels are burnt

Answer 15

there is a large heat output. exothermic reactions

Question 16

enthalpy channge

Answer 16

when you measure a heat change at constant pressure

Question 17

standard conditions for measuring enthalpy changes

Answer 17

• pressure of 200kPa
• temperature of 298K

Question 18

What does pressure effect

Answer 18

the amount of heat energy given out by reactions that involve gases. if a gas is given out some energy is required to away the atmosphere

Question 19

what do physical states affect

Answer 19

enthalpy change of a reaction

Question 20

enthalpy level diagrams

Answer 20

used to represent enthalpy change
- show the relative enthalpy levels of reactants and the products.
- vertal axis = enthalpy
- hrizontal axis = extent of reaction

Question 21

general name for enthalpy change for any reaction

Answer 21

standard molar enthalpy change of reaction

Question 22

standard molar enthalpy of formation

Answer 22

the enthalpy change when one mole substance is formed from its constituent elements under standard conditions, all reactants and products being in their standard states

Question 23

standard molar enthalpy of combustion

Answer 23

the enthalpy change when one mole of substance is completely burnt in oxygen under standard conditions, all reactants and products being in their standard states

Question 24

what is temperature related to

Answer 24

the average kinetic energy of the particles in the system

Question 25

what is heat a measure of

Answer 25

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

Question 26

how do you measure enthalpy change

Answer 26

arrange for the heat to be transferred to a particular ass of a substantance, often water, then you need to know three things - mass of substance being heated or coolled - temperature change - specific heat capacity of the substance

Question 27

what is specific heat capacity

Answer 27

the amount of heat needed to raise the temperature of 1g of subtance by 1K

Question 28

what does a calorimeter do

Answer 28

finds the apporximate enthalpy change when a fuel burns

Question 29

what equation can we use instead of a calorimeter

Answer 29

q=mc(change in)T

Question 30

what is a flame calorimeter

Answer 30

an improved version of the simple calorimeter used for measuring enthalpy changes of combustion - spiral chimmney made of copper - the flame is enclosed - the fuel burns in pure oxygen rather than air