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3 years ago

What is the difference between physical and chemical changes?

1 answer:

4 0

In physical changes, the chemical makeup of an atom stays the same, like water turning into ice or steam, everything is still water but a different physical form. A chemical change is where an atom’s chemical make up does change, like wood burning to become soot, which is not wood, or photosynthesis, where carbon dioxide and water turn into a carbohydrate and oxygen

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A drop of water (H20) has a mass of 2.34 x 10e-2 grams. How many

creativ13 [48]

Answer:

2333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333

Explanation:

2x3=1000

3 0

3 years ago

The The thermal conductivity of a sheet of rigid, extruded insulation is reported to be k=0.029 W/ m measured temperature differ

vfiekz [6]

Answer:

Heat flux = 13.92 W/m2

Rate of heat transfer throug the 3m x 3m sheet = 125.28 W

The thermal resistance of the 3x3m sheet is 0.0958 K/W

Explanation:

The rate of heat transfer through a 3m x 3m sheet of insulation can be calculated as:

$q=-k*A*\frac{\Delta T}{\Delta X}\\\\q=-0.029\frac{W}{m*K}*(3m*3m)*\frac{12K}{0.025m} =125.28W$

The heat flux can be defined as the amount of heat flow by unit of area.

Using the previous calculation, we can estimate the heat flux:

$heat \, flux=\frac{q}{A}=\frac{125.28 W}{9 m^{2} } =13.92 W/m^{2}$

It can also be calculated as:

$q/A=-k*\frac{\Delta T}{\Delta X}$

The thermal resistance can be expressed as

$\Delta T=R_t*Q\\R_t=\Delta T/Q=\frac{\Delta X}{k*A}$

For the 3m x 3m sheet, the thermal resistance is

$R_t = \frac{\Delta X}{k*A}=\frac{0.025m}{0.029W/mK*9m^{2}}=0.0958 \, K/W$

4 0

3 years ago

If acetic acid is the only acid that vinegar contains (ka=1.8×10−5), calculate the concentration of acetic acid in the vinegar.

kicyunya [14]

Ethanoic (Acetic) acid is a weak acid and do not dissociate fully. Therefore its equilibrium state has to be considered here.

$CH_{3}COOH \ \textless \ ---\ \textgreater \ H^{+} + CH_{3}COO^{-}$

In this case pH value of the solution is necessary to calculate the concentration but it's not given here so pH = 2.88 (looked it up)

pH = 2.88 ==> $[H^{+}]$ = $10^{-2.88}$ = 0.001 $moldm^{-3}$

The change in Concentration Δ $[CH_{3}COOH]$ = 0.001 $moldm^{-3}$

  CH3COOH H+ CH3COOH
Initial   $moldm^{-3}$      $x$ 0 0

Change $moldm^{-3}$ -0.001 +0.001 +0.001

Equilibrium $moldm^{-3}$ $x$ - 0.001 0.001 0.001


Since the $k_{a}$ value is so small, the assumption
$[CH_{3}COOH]_{initial} = [CH_{3}COOH]_{equilibrium}$ can be made.

$k_{a} = [tex]= 1.8*10^{-5} = \frac{[H^{+}][CH_{3}COO^{-}]}{[CH_{3}COOH]} = \frac{0.001^{2}}{x}$

Solve for x to get the required concentration.

note: 1.)Since you need the answer in 2SF don&t round up values in the middle of the calculation like I've done here.

2.) The ICE (Initial, Change, Equilibrium) table may come in handy if you are new to problems of this kind

Hope this helps!

8 0

3 years ago

Choose the following statements that show evidence for a chemical reaction.

Leno4ka [110]

Explanation:

A chemical reaction is defined as the reaction in which bonds between the reactants either break or form which leads to the formation of a new substance.

For example, $2Li + Cl_{2} \rightarrow 2LiCl$

So, when we drop a sodium metal into water then it produces a frizzing sound which shows the metal is reacting with water.

We know that when two aqueous solutions chemically react with each other then it may lead to the formation of an insoluble substance which is known as precipitate.

This means that formation of a precipitate is also a chemical reaction.

Thus, we can conclude that following are the statements which show evidence for a chemical reaction.

Dropping sodium metal into water produces fizzing.

Mixing two aqueous solutions produces a precipitate.

8 0

4 years ago

A chemist needs to find the concentration of a solution of barium hydroxide.

Brums [2.3K]

Method 1: gravimetry

advantages: Impurities in the sample can be identified

disadvantages: The process is long, because it goes through several stages

Method 2: titration

advantages: the process is fast, because the titrate and titrant react immediately

disadvantages: Sometimes the determination of the end point of the titration is carried out too fast or too slowly so that the calculations carried out are inaccurate

3 0

2 years ago