7. D. 668 joules
8. B. 3 grams
<h3>Further explanation</h3>
Given
2 grams of water
6768 joules of energy
Required
Energy
Mass of water
Solution
The heat to change the phase can be formulated :
Q = m.Lf (melting/freezing)
Q = m.Lv (vaporization/condensation)
Lf=latent heat of fusion
Lv=latent heat of vaporization
7. phase change (ice to water)⇒Heat of fusion water=334 J/g
Q = 2 g x 334 J/g
Q = 668 J
8. phase change(water to vapor)⇒heat of vaporization water=2260 J/g
6768 J = m x 2260 J/g
m = 3 g
Answer:
ph = 4.73
Explanation:
Determine the pH of a 0.62 M NH4NO3 solution at 25C
The Kb for NH3 is 1.76 x 10^-5
NH4+ is the conjugate acid of the base NH3
Ka for NH4+ = K water / K NH3 conjugate base
Ka = 1 × 10⁻¹⁴ / 1.76 10⁻⁵
= 5.68 × 10⁻¹⁰
which is he Ka for
NH4 + H2O --> NH4OH + H⁺
Ka = [NH4OH] [H+] / [NH4)+]
5.68 × 10⁻¹⁰ = [X] [X] / [0.62]
X² = 3.52 × 10⁻¹⁰
X = [H+] = 1.88 × 10⁻⁵
p of that H+ = 4.73
ph = 4.73