chemistry - temperature changes

Question 1

how can you investigate the temperature change when different volumes of NaOH are added to HCl?

Answer 1

• measure 25cm^3 of HCl into a polystyrene cup
• measure the starting temperature of HCl
• add 5cm^3 of NaOH to the cup
• then stir the mixture and measure the maximum temperature reached ~ record in a table
• repeat the experiment with increasing volumes of NaOH

Question 2

why might calculated energy values be different to a data book?

Answer 2

energy gets lost to the surroundings

Question 3

if a reaction is exothermic, will a thermometer record an increase or decrease in temperature?

Answer 3

the thermometer will record an increase in temperature as energy will have been transferred to the surroundings

Question 4

how could you reduce the amount of heat lost to the surroundings?

Answer 4

• mix the reactants in a polystyrene cup
• place the polystyrene cup in a beaker of cotton wool
• lid on the cup to reduce energy lost by evaporation

Question 5

how could you ensure that the two reactants in separate test tubes were the same starting temperature?

Answer 5

• place them in a water bath at 25°C
• use a thermometer to ensure the reactants are the same temperature

Question 6

how can the temperature be measured more precisely and more reliably?

Answer 6

more precise: use a digital thermometer
more reliable: repeat the experiment and calculate a mean temperature measurement

Question 7

how could you test the effect of acid concentration on the energy released in a neutralisation reaction?

Answer 7

• place both reactants in a water bath so they are the same temperature, record this temperature
• add the alkali to the acid and record the final temperature
• calculate the temperature change
• repeat the process using different concentrations of acid
• record the results for each concentration in a table

Question 8

What must be controlled when testing the effect of acid concentration in a neutralisation reaction?

Answer 8

• alkali concentration
• alkali volume
• acid volume
• initial temperatures of each reactant
• external temperatures

Question 9

How do you know when a reaction is complete?

Answer 9

Mass of reaction mixture/volume of gas/ colour remains the same