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3 years ago

8 points

Chemistry

2 answers:

AveGali [126]3 years ago

8 0

Burning fossil fuels
Mining

Vladimir79 [104]3 years ago

6 0

Answer:

Burning fossil fuels

Mining

Using fertilizers

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True or false:The Earth's climate is changing. True False

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The answer is true.

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What is the half-life of an isotope that decays to 12.5% of its original activity in 19.8 hours?

katen-ka-za [31]

$x= x_{0} e^{kt} ,where~ x ~is~ the ~ |amount\ of \material\ at\ any~~time~t
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$and~ x_{0} ~the~original~amount.$
$when~x= \frac{12.5}{100} x_{0} }= \frac{125}{1000} x_{0}$
$\frac{x}{ x_{0} } = \frac{125}{1000}= \frac{1}{8}$
$when t=19.8 hrs,
x= x_{0} e^{19.8 k}, 
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$ln1-ln8=19.8k,
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-3 ln2=19.8k
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 \frac{x}{ x_{0} } = e^{ \frac{- ln 2}{6.6}t } 
$ $\frac{1}{2} = e^{ \frac{- ln2}{6.6}t } = \frac{1}{ e^{ \frac{ln 2}{6.6} t} } ,
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4 years ago

Nitrogen gas effuses through an opening 1.59 times faster than an unknown gas.

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A) Nitrogen has an ATOMIC mass number of 14, but nitrogen gas consists of N₂ molecules, so the mass to use in this problem is 28 g/mol. Rates of effusion ∝ 1/√(mass), so

√(mass unknown) /√28 = (rate N₂ effusion)/(rate unknown effusion) = 1.59 
∴ mass unknown = (1.59)²(28) = 70.78 g/mol 

B) One possible gas that comes close for this mass is NF₃.

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3 years ago

Is it possible for a solution to have negative pH values?

aleksandr82 [10.1K]

Answer:

Yes.

Explanation:

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What is the change in internal energy ( ΔU ) of the system if q = –8 kJ and w = –1 kJ for a certain process?

Radda [10]

Answer:

Change in internal energy (ΔU) = -9 KJ

Explanation:

Given:

q = –8 kJ [Heat removed]

w = –1 kJ [Work done]

Find:

Change in internal energy (ΔU)

Computation:

Change in internal energy (ΔU) = q + w

Change in internal energy (ΔU) = -8 KJ + (-1 KJ)

Change in internal energy (ΔU) = -8 KJ - 1 KJ

Change in internal energy (ΔU) = -9 KJ

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