Question

A 2.5 g piece of lithium metal is dropped into a 500.0 g sample of water at 22.1°C. The temperature of the water increases to 23.5°C. a. Is the reaction between lithium and water endothermic or exothermic? Explain. b. How much heat energy is released in the reaction? c. What is the heat released by the reaction in kJ/g of lithium?

Answer 1

Hi there,

1)

Lithium reacts violently with water and produces heat energy, hydrogen gas, and lithium hydroxide

2 Li(s) + 2 H2O(l) => 2 LiOH(aq) + H2(g)

Answer: Lithium reaction with water is exothermic (heat released), because metallic bond breaks in lithium metal and solvolysis (hydrolysis) releases energy.

2)

we have to use the equation

Q = m x Cs x ΔT

mcΔT = Q: m = mass; c = specific heat: ΔT = temp. difference; Q = Heat absorbed or Released.

Q = 500 g x 4.184 J/g.0C x (23.5 - 22.1) 0C = 2928.8 J

Energy released = 2929 J = 2.93 kJ

3)

from above energy released = 2.93 kJ ( 1 kJ = 1000 J)

heat released by lithium in reaction = 2.93 kJ / 2.5 g = 1.17 kJ/g

heat released by lithium in reaction = 1.17 kJ/g

Hope this helped you!

Thank You So Much!

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