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3 years ago

How much energy is required to melt 35.4 g of gold?

Chemistry

1 answer:

kap26 [50]3 years ago

4 0

Answer:

To determine the amount of heat the gold has absorbed to melt, we simply multiply the mass of the block of ice to the heat of fusion of water which is given above. We calculate as follows:

Heat = 20.0 g (35.4 g)

Heat = 1290 J

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An unknown solution has a pH of 7.2. Which of these chemicals is likely to cause the greatest decrease in the pH of the solution

prohojiy [21]

Answer:

HNO₃.

Explanation:

It is known that acids decrease the pH of the solution, while bases increase the pH of the solution.

So, HF and HNO₃ decrease the pH of the solution as they produce H⁺ in the solution.

While, KOH and NH₃ increase the pH of the solution as they produce OH⁻ in the solution.

HNO₃ will decrease the pH of the solution greater than HF.

Because HNO₃ is strong acid that decomposes completely to produce H⁺ more than the same concentration of HF that is a weak acid which does not decomposed completely to produce H⁺.

7 0

3 years ago

An exothermic reaction occurs spontaneously ,why?

Delvig [45]

Answer:

See below

Step-by-step explanation:

An exothermic reaction tends to occur spontaneously because the products are more stable than the reactants.

Nature tries to get to the lowest energy state.

4 0

2 years ago

Read the given equation. 2Na + 2H2O ? 2NaOH + H2 During a laboratory experiment, a certain quantity of sodium metal reacted with

emmasim [6.3K]

Answer:

The number of moles of Na metal that used initially = 0.70 mol.

The quantity of Na metal used initially to produce 7.80 of H₂ gas = 16.02 g.

Explanation:

It is a stichiometry problem.

2Na + 2H₂O → 2NaOH + H₂,

The balanced equation shows that 2.0 moles of Na metal react with 2.0 moles of water to produce 2.0 moles of NaOH and 1.0 mole of H₂,

Firstly, we need to convert the volume of H₂ (7.80 L) produced to no. of moles (n) using the ideal gas law: PV = nRT,

where, P is the pressure of the gas in atm (P at STP = 1.0 atm),

V is the volume of the gas in L (V = 7.80 L),

n is the number of moles in mole,

R is the general gas constant (R = 0.082 L.atm/mol),

T is the temperature of the gas in K (T at STP = 0.0 °C + 273 = 273.0 K).

∴ The number of moles of H₂ gas (n) = PV / RT = [(1.0 atm)(7.80 L)] / [(0.082 L.atm/mol.K)(273.0 K)] = 0.35 mol.

Using cross multiplication:

2.0 moles of Na will produce → 1.0 mole of H₂, from the stichiometrey.

??? moles of Na will produce → 0.35 mole of H₂.

∴ The number of moles of Na metal that used initially = (2.0 mol)(0.35 mol) / (1.0 mol) = 0.70 mol.

Now, we can get the quantity of Na metal using the relation:

∴ mass = n x molar mass = (0.70 mol)(22.989 g/mol) = 16.02 g.

6 0

3 years ago

The glow emitted by a substance exposed to eternal radiation is called

wolverine [178]

The glow emitted by a substance exposed to external radiation is called 'fluorescence'. In fluorescence, a fluorophore is exposed to external radiation, absorbs the energy and emits a form of light or glow. The answer to this question is 'fluorescence'. I hope this helps.

3 0

3 years ago

7. A human's appendix, wisdom teeth, and a dew claw are

Ugo [173]

Answer:

Vestigial Structures

Explanation:

Structures that were needed for an organism's ancestor, but no longer required for survival for the current organism. We needed our wisdom teeth and appendix in order to eat tougher foods, but now we do not need those to survive. But, we still have them.

8 0

2 years ago