Question

A student investigates the reaction between calcium carbonate and dilute hydrochloric acid.
Fig. 5.1 shows the apparatus the student uses.

The student measures the volume of gas in the gas syringe every 20 seconds. Fig. 5.2 shows a graph of the student’s results.

(a) State the name of the gas made in this reaction.
……………………………………………………………………………………………………………………………
(b) Complete the sentence.
The reaction is fastest between …………. seconds and …………. seconds.

(c) The total volume of gas made in the experiment is 50cm$^{3}$.
Calculate the total number of moles in 50cm$^{3}$ of the gas measured at room temperature and pressure (r.t.p.).
The volume of one mole of any gas is 24dm$^{3}$ at r.t.p.
Show your working.
                                            number of moles in 50cm$^{3}$ of the gas = ………………………….

(d) The student repeats the experiment using dilute hydrochloric acid at a higher temperature.
Explain why the reaction is faster.
Use ideas about collisions between particles.
…………………………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………………………

(e) The reaction between calcium carbonate and dilute hydrochloric acid is exothermic.
Complete Fig. 5.3 to show an energy level diagram for an exothermic reaction.
Label the activation energy and the energy change on your diagram.

 

▶️Answer/Explanation

Ans:  5(a) carbon dioxide ; 
5(b) the reaction is fastest between 0 seconds and 16 seconds ; 
5(c) (50 cm$^{3}$ =) 0.050 dm$^{3}$ ;
(moles = 0.050 ÷ 24) = 0.0021 ;
OR
(24 dm$^{3}$ =) 24 000 cm$^{3}$ ;
moles = (50 / 24000 =) 0.0021 ;

5(d) molecules have higher (average) energy/molecules are moving faster ;
more molecules with activation energy ;
frequency of collision (of molecules) is higher/more collisions per second/
more successful collisions ;

5(e)

products shown below reactants ;
energy change or ΔH correctly clearly indicated and labelled ;
activation energy clearly indicated and labelled ;