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3 years ago

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When oxygen reacts with hydrogen, it has the capacity to release 29 kilojoules of energy. Inside a fuel cell, oxygen reacts with

hydrogen to produce 23 kilojoules of useful energy. The rest of the energy is lost as heat. What’s the efficiency percentage of the fuel cell?

1 answer:

Vanyuwa [196]3 years ago

7 0

Answer:

79

Explanation:

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SnO2 + 2 H2 ——> Sn + 2 H2O

SpyIntel [72]

Answer:

0.15g

Explanation:

Given parameters:

Number of molecules of water = 1.2 x 10²¹ molecules

Unknown:

Mass of SnO₂ = ?

Solution:

To solve this problem, we have to work from the known to the unknown specie;

SnO₂ + 2H₂ → Sn + 2H₂O

Ensure that the equation given is balanced;

Now,

the known species is water;

6.02 x 10²³ molecules of water = 1 mole

1.2 x 10²¹ molecules of water = $\frac{1.2 x 10^{21} }{6.02 x 10^{23} }$ = 0.2 x 10⁻²moles

Number of moles of water = 0.002moles

From the balanced chemical equation:

2 mole of water is produced from 1 mole of SnO₂

0.002 moles of water will be produced from $\frac{0.002}{2}$ = 0.001moles

To find the mass;

Mass = number of moles x molar mass

Molar mass of SnO₂ = 118.7 + 2(16) = 150.7g/mol

Mass = 0.001 x 150.7 = 0.15g

3 0

3 years ago

Corrections here: 1. When calcium reacts with water, the temperature changes from 18c to 39c

Ugo [173]

When calcium reacts with water, the temperature changes from 18c to 39c is an exothermic reaction as energy is releasing and increasing the temperature.

<h3>What is an exothermic reaction?</h3>

Exothermic reaction are those reactions in which energy is released when a reaction completes.

An example is burning of wood.

Thus, when calcium reacts with water, the temperature changes from 18c to 39c is an exothermic reaction as energy is releasing and increasing the temperature.

Learn more about exothermic reaction

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3 0

2 years ago

The chemical equation shown represents photosynthesis. Carbon dioxide plus A plus light with a right-pointing arrow towards B pl

astra-53 [7]

Answer: <u><em>Option B; It traps light energy and converts it into chemical energy.</em></u>

<h2>Explanation: This substance is chlorophyll. It is a pigment present in leaves of all plants. It absorbs light energy and provides it to carry out the process of photosynthesis. Light energy is converted into chemical energy, in form of NADPH and ATP, which can be used by plants for photosynthesis.</h2><h2></h2><h2>This pigment is present only in plants, so option A is incorrect.</h2><h2></h2><h2>This pigment only absorbs and transfers energy to other molecules, and is not associated with carbon dioxide directly, so option C and D are also incorrect.</h2>

3 0

2 years ago

A student states that an exothermic chemical reaction can transfer its heat only by convection and conduction. Which disproves t

Over [174]

b is the right answer

6 0

3 years ago

Read 2 more answers

What is the osmotic pressure of a solution made from 22.3 g of methanol (MM = 32.04 g/mol) that was added to water to make 321 m

xxMikexx [17]

Answer: The osmotic pressure of a solution is 53.05 atm

Explanation:

To calculate the concentration of solute, we use the equation for osmotic pressure, which is:

$\pi=iMRT$

Or,

$\pi=i\times \frac{\text{Mass of solute}\times 1000}{\text{Molar mass of solute}\times \text{Volume of solution (in mL)}}\times RT$

where,

$\pi$ = osmotic pressure of the solution = ?

i = Van't hoff factor = 1 (for non-electrolytes)

Mass of solute (methanol) = 22.3 g

Volume of solution = 321 mL

R = Gas constant = $0.0821\text{ L.atm }mol^{-1}K^{-1}$

T = temperature of the solution = $25^oC=[273+25]=298K$

Putting values in above equation, we get:

$\pi=1\times \frac{22.3\times 1000}{32.04\times 321}\times 0.0821\text{ L.atm }mol^{-1}K^{-1}\times 298K$

$\pi=53.05atm$

Hence, the osmotic pressure of a solution is 53.05 atm

7 0

3 years ago