Chemistry, 20.11.2019 19:31 Masielovebug

Heat is added to a 200.-gram sample of h2o(s) to melt the sample at 0°c. then the resulting h2o ( ) is heated to a final temperature of 65°c. determine the total amount of heat required to completely melt the sample. heat is added to a 200.-gram sample of h2o(s) to melt the sample at 0°c. then the resulting h2o ( ) is heated to a final temperature of 65°c. determine the total amount of heat required to completely melt the sample.

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Answer from: thefandomarmy24

$\boxed{{\text{121}}{\text{.188 kJ}}}$ of energy is required to melt the sample completely.

Further explanation:

Heat of fusion is the amount of energy needed to melt a solid at its melting point. It is represented by $\Delta {H_{\text{f}}}$ .

Step 1: The ice at ${\text{0 }}^\circ {\text{C}}$ is converted to water at $0{\text{ }}^\circ {\text{C}}$ .

The formula to calculate the amount of energy is as follows:

${\text{Q}} = {\text{n}}\Delta {H_{\text{f}}}$ ...... (1)

Here,

Q is the amount of heat required.

n is the number of moles of water.

$\Delta {H_{\text{f}}}$ is the heat of fusion of ice.

The formula to calculate the moles of water is as follows:

${\text{Moles of water}}=\dfrac{{{\text{Given mass of water}}}}{{{\text{Molar mass of water}}}}$ ...... (2)

Substitute 200 g for the given mass of water and 18 g/mol for the molar mass of water in equation (2).

$\begin{aligned}{\text{Moles of water}}&=\frac{{200{\text{ g}}}}{{{\text{18 g/mol}}}}\\&= 11.11{\text{ mol}}\\\end{aligned}$

Substitute 11.11 mol for n and 6.01 kJ/mol for $\Delta\text{H}_\text{f}$ in equation (1).

$\begin{aligned}{{\text{Q}}_1}&= \left( {{\text{11}}{\text{.11 mol}}} \right)\left( {\frac{{6.01{\text{ kJ}}}}{{1{\text{ mol}}}}} \right)\\&= 66.77{\text{ kJ}}\\\end{aligned}$

Step 2: The temperature of water is raised from $0{\text{ }}^\circ {\text{C}}$ to $65{\text{ }}^\circ {\text{C}}$ .

The formula to calculate the heat energy of steam is as follows:

$\text{Q}=\text{mc}\Delta\text{T}$ …… (3)

Here,

Q is the amount of heat transferred.

m is the mass of substance.

c is the specific heat of substance.

$\Delta\text{T}$ is the temperature change.

The temperature change for the above change can be calculated as follows:

$\begin{aligned}\Delta\text{T}&=65\;^\circ\text{C}-0\;^\circ\text{C}\\&=65\;^\circ\text{C}\end{aligned}$

Substitute 200 g for m, $65\;^\circ\text{C}$ for $\Delta\text{T}$ and $4.186\;\text{j/g}^\circ\text{C}$ for c in equation (3).

$\begin{aligned}{{\text{Q}}_2} &= \left( {{\text{200 g}}} \right)\left( {{\text{4}}{\text{.186 J/g }}^\circ {\text{C}}} \right)\left( {{\text{65 }}^\circ {\text{C}}} \right)\\&= 54418{\text{ J}}\\\end{aligned}$

This energy is to be converted into kJ. The conversion factor for this is,

$1{\text{ J}} = {10^{ - 3}}{\text{ kJ}}$

Therefore the energy can be calculated as follows:

$\begin{aligned}{{\text{Q}}_{\text{2}}}&= \left( {54418{\text{ J}}} \right)\left( {\frac{{{{10}^{ - 3}}{\text{ kJ}}}}{{1{\text{ J}}}}} \right)\\&= 54.418{\text{ kJ}}\\\end{aligned}$

The total amount of energy can be calculated as follows:

$\text{Q}=\text{Q}_1+\text{Q}_2$ ...... (4)

Here, Q is the total energy and $\text{Q}_1$ ,and $\text{Q}_2$ are the values of energies calculated in first and second step respectively.

Substitute 66.77 kJ for $\text{Q}_1$ and 54.418 kJ for $\text{Q}_2$ in equation (4).

$\begin{aligned}{\text{Q}} &= 66.77{\text{ kJ}} + 54.418{\text{ kJ}}\\&= {\text{121}}{\text{.188 kJ}}\\\end{aligned}$

Learn more:

What is the enthalpy of the given reaction? Find the enthalpy of decomposition of 1 mole of MgO:

Answer details:

Grade: Senior School

Chapter: Thermodynamics

Subject: Chemistry

Keywords: energy, Q1, Q2, Q, 54.418 kJ, 66.77 kJ, 121.88 kJ, m, c, temperature change, amount of heat, total energy.

Answer from: Quest

but know think of it in terms of bond breaking and bond making.

h–h + h–h + o=o ==> h–o–h + h–o–h

as you can see from the diagram, theoretically, more energy is released by forming water, than was absorbed in breaking up the original hydrogen and oxygen molecules.

the energy level of the fuel + oxygen is higher than that of water.

therefore the fuel + oxygen mixture has the potential to release potential chemical energy as heat energy or, crucially, electrical energy, if the reaction can be made to go via oxidation and reduction reactions involving electron transfer.

see this page for more details of the full bond energy calculations

a fuel cell is a device to make electricity that functions like an electrical cell or battery that you supply with a fuel (liquid or gas) and an oxidant (oxidising agent, usually oxygen gas) which react together in a redox reaction (oxidation + reduction) to release energy as a flow of electrons i.e. an electrical current capable of doing useful work.

the oxidation of the fuel and the reduction of the oxidant reactions take place on electrodes (see diagram on right, all fully explained further down the page).

fuel cells essentially a device to release the chemical potential energy of combustible fuels as electrical energy at a much lower temperature and without the flame!

so, the idea of a hydrogen–oxygen fuel cell is to release the energy from hydrogen reacting with oxygen, not as heat as in normal combustion in air, but as useful electrical energy i.e. a practical electricity supply.

hydrogen-oxygen fuel cells are much efficient than conventional power stations or batteries (e.g. zinc-carbon) because the electrical energy is directly generated from the chemical reaction between the oxidant and the fuel - there are no complications with boilers, turbines and generators.

in fossil fuel power stations, motor vehicles, coal/gas fires etc. quite a percentage of energy is lost as waste heat.

with a fuel cell there are fewer stages in producing the useful energy, so there is less opportunity to lose potentially useful energy e.g. waste heat, friction from moving parts etc.

a hydrogen–oxygen fuel cell is a non–polluting clean fuel since the only combustion product is water.

fuel cells do not produce pollutants like carbon monoxide, sulfur dioxide and nitrogen oxides - gases you get from fossil fuel combustion in power stations or burnt road vehicles..

cars powered by fuel cells would be quite an environmental advantage in cities, where electric cars are already beginning to be significantly used in developed countries.

fuel cells could replace larger batteries which are not easily recycled and contain highly toxic metal compounds.

it would be an ideal fuel on this basis e.g. for motor vehicles, but that's not the only factor to consider!

it would be ideal if the hydrogen fuel could be manufactured by electrolysis of water e.g. using solar cells.

hydrogen can be used to power fuel cells.

it all sounds wonderful but, still technological problems to solve for large scale manufacture and distribution of 'clean' hydrogen gas or use in generating electricity and its rather an inflammable explosive gas!

explanation:

fuel cells e.g. the hydrogen-oxygen fuel electrical cell

fuel cells have to be supplied by an external source of fuel (e.g. hydrogen) and an oxidant e.g. oxygen or air.

the hydrogen or any other fuel is oxidised electrochemically inside the fuel cell to produce a potential difference i.e. a voltage capable of producing a working current.

the overall chemical reaction in a hydrogen fuel electrochemical cell involves the oxidation of hydrogen by oxygen to produce only water.

hydrogen fuel cells offer an alternative to rechargeable cells and batteries.

a fuel cell will produce a potential difference ('voltage') and a workable electric current until one of the reactants is used up.

hydrogen gas can be used as fuel.

it burns with a pale blue flame in air reacting with oxygen to be oxidised to form water.

hydrogen + oxygen ==> water

2h2(g) + o2(g) ==> 2h2o(l)

Answer from: Quest

in 1783 cavendish was working with his hydrogen gas and found that when he burned it and condensed the vapor it was water. this was very significant since it disproved the greek theory of elements completely since water was not a simple substance but the product of two gases. it was lavoisier who hearing of the experiment gave cavendish's gas the name hydrogen ("water-producer") and added that hydrogen burned by combining with oxygen and that water was a hydrogen-oxygen combination.

explanation:

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Heat is added to a 200.-gram sample of h2o(s) to melt the sample at 0°c. then the resulting h2o ( )...

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