When Xavier places his hands near a light bulb, he notices that certain areas around the light bulb are warmer than others. Whic
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Answer:
The heat needed to boil 1 gallon of water is 81,490.62 Joules.
Explanation:
Where:
Q = heat absorbed or heat lost
c = specific heat of substance
m = Mass of the substance
ΔT = change in temperature of the substance
We have :
Volume of water = V = 1 gal = 4546.09 mL
Density of water , d= 1 g/mL
mass of water = m = d × V = 1g/mL × 4546.09 mL = 4546.09 g
Specific heat of water = c = 1 Cal/g°C
ΔT = 100°C - 25°C = 75 °C
9 (boiling pint of water is 100°C)
Heat absorbed by the water to make it boil:
1 calorie = 4.184 J
The heat needed to boil 1 gallon of water is 81,490.62 Joules.
A reaction is exothermic if Δ<em>H</em> (or in some textbooks) is negative:
- H₂ + Br → 2 HBr, ΔH < 0.
- CH₄ + 2 O₂ → CO₂ + 2 H₂O, ΔH < 0.
A reaction is endothermic if Δ<em>H</em> is positive:
- 2 NH₃ → N₂ + 3 H₂, ΔH > 0.
- 2 HCl → H₂ + Cl₂ ΔH > 0.
The enthalpy of a system is the sum of its internal energy. ΔH < 0 indicates that the reactants lose internal energy in the reaction. Energy conserves, and those internal energies must have converted to some other form of energy. They typically end up as thermal energy. The reaction will release heat since it is exothermic.
Similarly, ΔH > 0 indicates that the reactants gains internal energy in the reaction. Energy conserves. As a result, the reaction must have gained energy from its surroundings. The reaction will be endothermic since it absorbs heat.