energetics

Question 1

law of conservation of energy

Answer 1

the overall amount of energy does not change as energy is conserved in reactions- this means energy can’t be created or destroyed, only transferred

Question 2

exothermic reaction

Answer 2

releases heat energy

Question 3

endothermic reaction

Answer 3

takes in heat energy

Question 4

neutralisation reactions always

Answer 4

give energy out

Question 5

displacement reactions always

Answer 5

take energy in or give it out

Question 6

combustion reactions always

Answer 6

give energy out

Question 7

calorimetry is

Answer 7

a technique used to measure changes in enthalpy of chemical reactions

Question 8

two types of calorimetry experiments-

Answer 8

enthalpy changes of reactions in solution, enthalpy changes of combustion

Question 9

enthalpy changes of reactions in solution experiment

Answer 9

A fixed volume of one reagent is added to the calorimeter and the initial temperature taken with a thermometer
An excess amount of the second reagent is added and the solution is stirred continuously
The maximum temperature is recorded and the temperature rise calculated

Question 10

enthalpy changes of combustion experiments

Answer 10

A fixed volume of water is measured and transferred to the copper can
The spirit burner containing, for example, an alcohol, is weighed on a 2 d.p. balance
The initial temperature of the water is measured and recorded
The alcohol is ignited and the water is stirred continuously
When the temperature has risen by about 20 degrees the flame is extinguished and the spirit burner is re-weighed
The final temperature of the water is recorded

Question 11

sources of error in combustion experiment

Answer 11

Not all the heat produced by the combustion reaction is transferred to the water
Some heat is lost to the surroundings
Some heat is absorbed by the calorimeter

Question 12

to minimise the heat loss

Answer 12

copper calorimeter should not be placed too far above the flame and a lid placed over the calorimeter, shielding can be used to reduce draughts

Question 13

in combustion experiment the two main sources of error are

Answer 13

heat losses, incomplete combustion

Question 14

heat transferred=

Answer 14

mass of water x specific heat capacity x temp change

Question 15

heat energy change is calculated by

Answer 15

calculating the heat transferred

Question 16

molar enthalpy change =

Answer 16

heat change for the reaction / number of moles

Question 17

materials needed to investigate temperature change

Answer 17

Dilute hydrochloric acid
Dilute sodium hydroxide solution
Styrofoam (polystyrene) calorimeter & lid
25 cm3 measuring cylinder
Thermometer & stirrer

Question 18

method to investigate temperature change

Answer 18

Using a measuring cylinder, place 25 cm3 of the NaOH solution into the calorimeter
Measure and record the temperature of the solution
Add 5 cm3 of the dilute HCl and stir
Measure and record the highest temperature reached by the mixture
Repeat steps 1 – 4 increasing the amount of acid added by 5 cm3 each time

Question 19

evaluation of investigating temperature change

Answer 19

Plot a graph of the results and draw a line of best fit, using the graph to determine what volume of acid causes the biggest change in temperatureConclusion:
The larger the difference in the temperature the more energy is absorbed or released