Question

iii.
Define endothermic reaction. Give an example,
iv.
How much heat energy is necessary to raise the temperature of 10 kg of water from 40 °C to
100 °C?
If the speed of light in a medium is 2 x 10% m/s, what is the absolute refractive index of the
medium? (Velocity of light in vacuum = 3 x 10 m/s)​

Answer 1

exothermic reaction occurs when the temperature of a system increases due to the evolution of heat. This heat is released into the surroundings, resulting in an overall negative quantity for the heat of reaction ( qrxn<0 ). An endothermic reaction occurs when the temperature of an isolated system decreases while the surroundings of a non-isolated system gains heat. Endothermic reactions result in an overall positive heat of reaction ( qrxn>0 ).

Exothermic and endothermic reactions cause energy level differences and therefore differences in enthalpy ( ΔH ), the sum of all potential and kinetic energies. ΔH is determined by the system, not the surrounding environment in a reaction. A system that releases heat to the surroundings, an exothermic reaction, has a negative ΔH by convention, because the enthalpy of the products is lower than the enthalpy of the reactants of the system.

C(s)+O2(g)⟶CO2(g)(ΔH = –393.5 kJ)

H2(g)+12O2(g)⟶H2O(l)(ΔH = –285.8 kJ)

The enthalpies of these reactions are less than zero, and are therefore exothermic reactions. A system of reactants that absorbs heat from the surroundings in an endothermic reaction has a positive ΔH , because the enthalpy of the products is higher than the enthalpy of the reactants of the system.

N2(g)+O2(g)⟶2NO(g)(ΔH = +180.5 kJ > 0)

C(s)+2S(s)⟶CS2(l)(ΔH = +92.0 kJ > 0)

Because the enthalpies of these reactions are greater than zero, they are endothermic reactions.

Answer 2

Answer:

Endothermic reactions are chemical reactions in which the reactants absorb heat energy from the surroundings to form products. These reactions lower the temperature of their surrounding area, thereby creating a cooling effect. Physical processes can be endothermic as well – Ice cubes absorb heat energy from their surroundings and melt to form liquid water