Seeing signs of a chemical reaction does not always mean that a reaction is happening. For example, a gas (water vapor) is given off when water boils. ... You can tell that it is a physical change because water vapor can condense to form liquid water. In a chemical change, a new substance must be produced.
Answer: 20.7 kJ
Explanation:
According to first law of thermodynamics:
=Change in internal energy
q = heat absorbed or released
w = work done or by the system
w = work done on the system=
{Work is done on the system is positive as the final volume is lesser than initial volume}
w = 4.51 kcal =
(1kcal = 4.184kJ)
q = +1.79 kJ {Heat absorbed by the system is positive}

Thus
for a system that receives 1.79 kJ of heat from surroundings and has 4.51 kcal of work done on it at the same time is 20.7 kJ
You can eliminate A, C, and D almost instantly if you know that engineers are construction workers. The answer is B.
Answer:
Al2O3 + H2SO4 = Al2(SO4)3 + H2O
Explanation:
On adding salt.....The boiling temperature increases.....
So ∆t= KB * molality
=O.52*(58/58)/4
= O.52*1/4
= 0.13
So increase is 100+.13=100.13°c