Physical Chemistry

Question 1

what changes when chemical reactions occur?

Answer 1

there is a change in energy

Question 2

what is an exothermic reaction?

Answer 2

it is a reaction that gives out energy to the surroundings usually in the form of heat and usually shown by a rise in temperature of the surroundings

Question 3

what is an endothermic reaction?

Answer 3

it is a reaction that takes energy from the surrounding, usually in form of heat and usually shown by a fall in temperature of the surroundings

Question 4

what is the name of the overall change in energy of a reaction?

Answer 4

Enthalpy change

Question 5

what is the symbol of the enthalpy change?

Answer 5

(triangle)H

Question 6

what is the unit of enthalpy change?

Answer 6

kl/mol (the amount of kilojoules per mole

Question 7

can an enthalpy change be positive?

Answer 7

yes it can have a positive but also negative value

Question 8

what causes an enthalpy change to be negative?

Answer 8

if the reaction is exothermic since it is giving out energy

Question 9

what causes an enthalpy change to be positive?

Answer 9

if the reaction is endothermic since it is taken in energy

Question 10

what is a calorimetry used for?

Answer 10

to measure the amount of energy transferred in a chemical reaction with a pretty simple equipment.

Question 11

how do you measure the amount of energy transferred in reactions?
(calorimetry practical)

Answer 11

you take the temperature of the reactants, mix them and measure the temperature of the solution at the end of the reaction

Question 12

how do you investigate the enthalpy change of dissolving, displacement or neutralisation reactions?
(calorimetry practical)

Answer 12

by mixing the reactants in a polystyrene cup

Question 13

what is the biggest problem with energy measure?

calorimetry practical

Answer 13

the amount of energy lost to the surrounding

Question 14

how can you reduce the loss of energy?

calorimetry practical

Answer 14

by putting the polystyrene cup into a beaker of cotton wool to give more insulation, and putting a lid on the cup to reduce energy lost by evaporation

Question 15

EXAMPLE (calorimetry practical)
describe how a calorimetry practical for neutralisation reaction between hydrochloric acid and sodium hydroxide would look like
(there are 4 steps)

Answer 15

1) put 25cm3 of hydrochloric acid and sodium hydroxide in separate beakers
2) place the beakers in a water bath set to 25 degrees C until they are both at the same temperature (25 degrees C)
3) add the hydrochloric acid followed by the sodium hydroxide to a polystyrene cup with a lid
4) take the temperature of the mixture every 30 seconds, and record the highest temperature