Chemistry, 23.09.2019 14:30 Deuce9024

What is the amount of heat energy released when 50.0 grams of water is cooled from 20.0°c to 10.0°c?

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Q = mc Δt
q= heat, m = mass (in grams), c=specific heat (4.18 J/°C * g or J/K * g for water), Δt = change in temperature (in kelvin)

For this equation:

q = ?, m = 50.0 g, c = 4.18 J/°C *g = 4.18 J/K *g, initial t = 20.0°C, final t = 10°C

To convert from °C to K, add 273 to °C
0°C = 273 K

Initial t = 20.0°C + 273 = 293 K
Final t = 10.0°C + 273 = 283 K

ΔT = final temperature - initial temperature = 283-293 = -10 K

Plug in what you know:

q = (50.0 g) x (4.18 J/K * g) x (-10 K) = -2090

Check sig figs and cancel out units:

-2090 J (you need 3 sig figs from the original numbers given and the units are Joules since grams and Kelvin cancel out)

Check to make sure answer makes sense:

Since heat energy is released, the answer should be negative. The answer is negative and therefore, makes sense

Answer from: Quest

as given the equation is

2al + 6 hcl > 2 alcl3 + 3 h2(g)

as per equation two moles of aluminum reacts with six moles of hcl to give two moles of alcl3 and three moles of hydrogen gas

given: three moles of al are present and 7 moles of hcl

for three moles of aluminum nine moles of hcl will be required

however as 7 moles of hcl are present so the limiting reagent is hcl

hcl is going to decide the number of moles of product formed

when six moles of hcl are present = 3 moles of h2 are formed

when one mole of hcl is present == 3/6 mole sof h2 will be formed

when 7 moles of hcl are present = 3 x 7/ 6 moles of h2 will be formed = 3.5 moles of h2

Answer from: Quest

the answer is b because, investigating whether another species of moth also drinks tears might be interesting, but it would not directly explain why this species of moth does.

to explain why this species of moth drinks tears, the scientist could ask: "what nutrients that moths need are in elephant tears? "

the scientist could experiment with moth repellent or oter ways to keep the moths away, but that would not answer his original question.

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