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3 years ago

Which statement best describes a physical change?

2 answers:

8 0

Answer: 3 Changes can occur to physical properties of a substance, but the chemical composition of the substance remains the same

Explanation:

Physical change mainly physical properties of a substance while the chemical changes remain unchanged. Once there is a change to the chemistry of the substance, this would be classified as a chemical change.

Nina [5.8K]3 years ago

3 0

The answer is 2 because the composition won’t change just the physical aspects

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What mass of salt would you need to add to 1.00kg of water to achieve a freezing point of -5 degrees C

Serga [27]

Answer:

The type of salt to be added to the water is not known from the question but no worries, I will try to give you the step by step procedure to answer any type of question similar to this.

To answer this question, we should know some facts.

1. the molar freezing point depression constant of water (Kf) = 1.86 K kg/mol

2. the molar mass of the salt if NaCl = 58.5 g/mol ; KCl = 74.5 g/mol

3. since the salt can dissociate if NaCl or KCl into two ions, the Van't Hoff factor ( i )= 2

Note that: the change in freezing point, molarity, deepression constant and van't Hoff factor are related by this formula;

ΔTf = i Kf m

So lets take NaCl as the salt:

Molar mass = 58.5 g/mol

Van't Hoff factor = 2

1. calculate the number of moles

So we can calculate the molarity of the salt NaCl from the formula;

m = ΔTf / i Kf

m = 5 / 2 * 1.86

m = 5 / 3.72

m = 1.344 mol/kg

2. calculate the number of moles of the salt required

Next is to multiply the molarity by the mass of water. Density of water = 1kg/L

number of moles = 1.344 mol/kg * 1 Kg/L * 1 kg water

number of moles = 1.344 moles.

3. calculate the mass of the salt.

numner of moles = mass / molar mass

mass = number of moles * molar mass

mass = 1.344 * 58.5

mass = 78.624 g of NaCl salt.

You can follow these steps to solve for the type of salt you are given in the question.

6 0

4 years ago

Balance the following redox reaction if it occurs in H2SO4. What are the coefficients in front of C3H8O2 and H2SO4 in the balanc

Mrac [35]

Answer:

3C3H8O2 and 16H2SO4

Explanation:

C3H8O2(aq) + K2Cr2O7(aq) → C3H4O4(aq) + Cr2(SO4)3(aq)

In acidic reaction you need to separate the half-reactions knows.

C3H8O2(aq) → C3H4O4(aq)

Cr2O7(2-) → Cr(+3) (aq)

Balance elements other than O and H. Add H2O to balance oxygen, balance hydrogen by adding protons (H+) and Balance the charge of each equation with electrons

C3H8O2(aq) + 2H2O(l) → C3H4O4(aq) + 8H(+) + 8e(-)

Cr2O7(2-) + 14H(+) + 6e(-) → 2Cr(+3) + 7H2O (aq)

Scale the reactions so that the electrons are equal. If not look for a common multiple. In this case is 24, 8*3=6*4. So for each equation multiply for the correct multiple. Then

3C3H8O2(aq) + 6H2O(l) → 3C3H4O4(aq) + 24H(+) + 24e(-)

4Cr2O7(2-) + 56H(+) + 24e(-) → 8Cr(+3) + 28H2O (aq)

Add the reactions and cancel out common terms and group the ions in compounds if u can.

3C3H8O2(aq) + 32H(+) + 4Cr2O7(2-) → 3C3H4O4(aq) + 4Cr2(SO4)3(aq) + 22H2O (aq)

We are in acidic medium so the H(+) must be from H2SO4. So 32H(+) is 16H2SO4 in reactives. Add SO4(2-) in products and balance

16H2SO4 +3C3H8O2(aq) + 4Cr2O7(2-) → 3C3H4O4(aq) 4Cr2(SO4)3(aq) + 22H2O (aq) + 4SO4(2-)

Then

16H2SO4 +3C3H8O2(aq) + 4Cr2O7(2-) → 3C3H4O4(aq) 4Cr2(SO4)3(aq) + 22H2O (aq) + + 2K2SO4 (aq)

8 0

4 years ago

Fill in the chart to identify three parts of Dalton's model of the atom.

mamaluj [8]

The first part of Dalton's model is that all matter is made of atoms, and these atoms are indivisible.

The second part of this model is that atoms of an element have identical masses and identical propertes.

At last, the third part of Dalton's model is that all compounds are formed by two or more different type of atoms combined.

6 0

1 year ago

How much heat will be absorbed by a 63.1 g piece of aluminum (specific heat = 0.930 J/g･°C) as it changes temperature from 23.0°

cluponka [151]

Answer:

$Q=2582J=2.58kJ$

Explanation:

Hello,

In this case, for us to compute the absorbed heat, we apply the following equation:

$Q=m_{Al}Cp_{Al}(T_2-T_1)$

Whereas we use the mass, specific heat and temperature change for the piece of aluminium, thus, we obtain:

$Q=63.1g*0.930\frac{J}{g*\°C}*(67.0-23.0)\°C\\ \\Q=2582J=2.58kJ$

It is positive as the heat is entering, therefore the temperature raises.

Best regards.

4 0

3 years ago

Write the formula of phosphorus iii iodide

goldenfox [79]

PI3 and SCl2 and CS2 and N2O5 there you go!

4 0

3 years ago

Read 2 more answers