Question

For the reaction A + 2B → C, 0.050 mol A and 0.10 mol B are mixed in aqueous solution in a coffee cup calorimeter containing a total of 50 mL of water. The temperature of the water increases by 5.5K. What is ΔH_rxn?

a. +1200 kJ/mol

b. -1.2 kJ/mol

c. -23 kJ/mol

d. none of the above

Answer 1

density of water = 1 g/mL
mass of water = (volume)*(density)
= 50*1
= 50 g

since, temperature of water increases
so, water absorbs energy
and hence, reaction is exothermic
heat absorbs by water = m*s*(delta T)
= 50*4.18*5.5
= 1149.5 J
= 1.1495 KJ

this heat is coming from the reaction taking place
so,
0.050 mole of A generate 1.1495 KJ of heat
1 mole of A generate (1.1495/0.050) KJ of heat
1 mole of A generate 23 KJ of heat
delta Hrxn = -23 KJ/mol

Answer : option c