If the heat of reaction is negative, that means that:

Chemistry

1 answer:

Crazy boy [7]3 years ago

4 0

Answer:

if the heat of reaction is positive, the reaction is said to be endothermic; if negative, exothermic.

Explanation:

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A geological sample is found to have a Pb-206/U-238 mass ratio of 0.337/1.00. Assuming there was no Pb-206 present when the samp

nikdorinn [45]

Answer:

2.1x10⁹ years

Explanation:

U-238 is a radioactive substance, which decays in radioactive particles. It means that this substance will lose mass, and will form another compound, the Pb-206.

The time need for a compound loses half of its mass is called half-life, and knowing the initial mass (mi) and the final mass (m) the number of half-lives passed (n) can be found by:

m = mi/2ⁿ

The mass of Pb-206 will be the mass that was lost by U-238, so it will be mi - m. Thus, the mass ration can be expressed as:

(mi-m)/m = 0.337/1

mi - m = 0.337m

mi = 1.337m

Substituing mi in the expression of half-life:

m = 1.337m/2ⁿ

2ⁿ = 1.337m/m

2ⁿ = 1.337

ln(2ⁿ) = ln(1.337)

n*ln(2) = ln(1.337)

n = ln(1.337)/ln2

n = 0.4190

The time passed (t), or the age of the sample, is the half-life time multiplied by n:

t = 4.5x10⁹ * 0.4190

t = 1.88x10⁹ ≅ 2.1x10⁹ years

5 0

3 years ago

Determine the number of grams of carbon dioxide that can be formed from 0.500 grams of iron oxide and an excess of carbon.

Nimfa-mama [501]

Taking into account the reaction stoichiometry, 0.2066 grams of CO₂ are formed from 0.500 grams of iron oxide and an excess of carbon.

<h3>Reaction stoichiometry</h3>

In first place, the balanced reaction is:

2 Fe₂O₃ + 3 C → 4 Fe + 3 CO₂

By reaction stoichiometry (that is, the relationship between the amount of reagents and products in a chemical reaction), the following amounts of moles of each compound participate in the reaction:

Fe₂O₃: 2 moles
C: 3 moles
Fe:4 moles
CO₂: 3 moles

The molar mass of the compounds is:

Fe₂O₃: 159.7 g/mole
C: 12 g/mole
Fe: 55.85 g/mole
CO₂: 44 g/mole

Then, by reaction stoichiometry, the following mass quantities of each compound participate in the reaction:

Fe₂O₃: 2 moles ×159.7 g/mole= 319.4 grams
C: 3 moles ×12 g/mole= 36 grams
Fe: 4 moles ×55.85 g/mole= 223.4 grams
CO₂: 3 moles ×44 g/mole= 132 grams

<h3>Mass of CO₂ formed</h3>

The following rule of three can be applied: if by reaction stoichiometry 319.4 grams of Fe₂O₃ form 132 grams of CO₂, 0.500 grams of Fe₂O₃ form how much mass of CO₂?

$mass of CO_{2} =\frac{0.500 grams of Fe_{2}O_{3}x132 grams of CO_{2} }{319.4 grams of Fe_{2}O_{3}}$