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3 years ago

15. Describe two physical and two chemical changes involved in cooking. (4 points)

Chemistry

1 answer:

Zigmanuir [339]3 years ago

8 0

Answer:

Explanation:

Physical changes in cooking include the melting of solids, such as butter, and the boiling of liquids, such as water. Examples of physical changes would be the melting of fats and the boiling of water. Chemical changes involve the production of new substances.

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In an electrically heated boiler, water is boiled at 140°C by a 90 cm long, 8 mm diameter horizontal heating element immersed in

RideAnS [48]

Explanation:

The given data is as follows.

Volume of water = 0.25 $m^{3}$

Density of water = 1000 $kg/m^{3}$

Therefore, mass of water = Density × Volume

= $1000 kg/m^{3} \times 0.25 m^{3}$

= 250 kg

Initial Temperature of water ( $T_{1}$ ) = $20^{o}C$

Final temperature of water = $140^{o}C$

Heat of vaporization of water ( $dH_{v}$ ) at $140^{o}C$ is 2133 kJ/kg

Specific heat capacity of water = 4.184 kJ/kg/K

As 25% of water got evaporated at its boiling point ( $140^{o}C$ ) in 60 min.

Therefore, amount of water evaporated = 0.25 × 250 (kg) = 62.5 kg

Heat required to evaporate = Amount of water evapotaed × Heat of vaporization

= 62.5 (kg) × 2133 (kJ/kg)

= $133.3 \times 10^{3}$ kJ

All this heat was supplied in 60 min = 60(min) × 60(sec/min) = 3600 sec

Therefore, heat supplied per unit time = Heat required/time = $\frac{133.3 \times 10^{3}kJ}{3600 s}$ = 37 kJ/s or kW

The power rating of electric heating element is 37 kW.

Hence, heat required to raise the temperature from $20^{o}C$ to $140^{o}C$ of 250 kg of water = Mass of water × specific heat capacity × (140 - 20)

= 250 (kg) × 40184 (kJ/kg/K) × (140 - 20) (K)

= 125520 kJ

Time required = Heat required / Power rating

= $\frac{125520}{37}$

= 3392 sec

Time required to raise the temperature from $20^{o}C$ to $140^{o}C$ of 0.25 $m^{3}$ water is calculated as follows.

$\frac{3392 sec}{60 sec/min}$

= 56 min

Thus, we can conclude that the time required to raise the temperature is 56 min.

4 0

3 years ago

Hydrogen is used as a rocket fuel because it is very light and reacts explosively and completely with oxygen. For the combustion

777dan777 [17]

Answer:

1. K<10−3

Explanation:

Equilibrium Constant is an expression which involves the concentration of the product divided by the concentration of the reactant molecules.

However the concentration of the pure liquid and pure solid is regarded as 1.

Equilibrium expression for the equation 2H2(g)+O2(g)⇌2H2O(g)

Equilibrium Constant = [H2O]^2/[H2]^2 x [O2]

Since H2O is a pure liquid, its concentration = 1

There fore;

Equilibrium Constant = 1/[H2]^2 x [O2]

This shows that the Equilibrium Constant of the equation will be less than 1 and greater than 0.

7 0

2 years ago

Balance the following Equation Show your work.

7nadin3 [17]

Answer:

1) alr balanced

2) 2 2 1

3) 2 1 1 2

4) 2 3 2

5) 2 1 2 1

6) 1 6 2 3

7) 2 2 1

8) 1 2 1 2

9) 2 5 4 6

10) 3 1 2

3 0

2 years ago

Which physical property is being used to separate the mixtures in each of the following cases?

kirill115 [55]

I think that this is

6 0

2 years ago

In a liquid-liquid extraction, how can you experimentally tell which layer is organic and which layer is aqueous? Can you always

zysi [14]

Answer:

Explanation:

Liquid-liquid extraction is a very useful method to separate components from a mixture. It consists of separating one or several substances dissolved in a solvent by transferring them to another solvent insoluble or partially insoluble in the first. The transfer of matter is achieved by direct contact between the two liquid phases.

For the extraction process, the solution is placed in a separating funnel, a water-immiscible organic solvent is added (ethyl ether is the most used), the solution with the compound to be separated, the funnel is covered and the funnel is top. Then it shakes. Depending on the solubilities and density, different layers are observed. The denser the compound, the more it will sink.

Since the organic compound is usually much more soluble in ether than in water, most of the organic compound will be dissolved in the ether phase (upper phase) and inorganic salts, which are not soluble in ether, will remain in the aqueous phase ( lower phase). Subsequently, by separating the separating funnel the two phases are separated, the organic phase is collected.

Occasionally, after stirring, the two immiscible liquids do not separate sharply, forming an emulsion in the intermediate zone. This is called the colloidal suspension of a liquid in another (system consisting of two or more phases, usually a liquid and another dispersed in the form of generally very fine solid particles). One of the reasons for the formation of an emulsion is when the two phases have similar densities. Then the relative density of the organic solvent and water cannot always be relied upon, although there are methods to facilitate the complete separation of the two phases.

7 0

2 years ago