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4 years ago

7

Why can't chemical changes be reversed?

1 answer:

Temka [501]4 years ago

7 0

<span>a chemical change results in the formation of one or more new substances</span>

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Perform the following

Setler [38]

35.1 i’m not sure it’s it’s correct but that’s what i got

5 0

3 years ago

When an atom gains or loses one or more electrons an ion is formed. question 2 options:

kozerog [31]

The answer is true, when an atom gains or loses one or more electrons an ion is, in fact, formed.

7 0

3 years ago

Calculate the mass percent of a NaCl solution in which 140g of NaCl is dissolved in 4.50L of water at 25C (density = 0.997g/mL).

Lemur [1.5K]

Mass percent is one way of expressing concentration of a solution. It is expressed as the mass of solute per mass of solution. For this case, mass percent is calculated as follows:

% mass = 140 g NaCl / (140 g NaCl + 4500 mL ( 0.997 g/mL)) x 100
% mass = 3.03 %

6 0

4 years ago

How much heat is needed to change the temperature of a 30.0 gram sample of copper from 20.0c to 60.0c?

guajiro [1.7K]

Answer: 462.00 Joules of heat will be needed to change the temperature of copper from 20° C to 60° C.

Explanation:

Mass of copper,m = 30.0 grams

Specific heat capacity of copper,c = $0.385 J/g ^oC$

$T_1=20^oC,T_2=60^oC$

$\Delta T=T_2-T_1=60^oC-20^oC=40^oC$

$Q=mc\Delta T$

$Q=30.0 grams\times 0.385 J/g ^oC\times 40^oC=462.00 J$

462.00 Joules of heat will be needed to change the temperature of copper from 20° C to 60° C.

6 0

4 years ago

I really need the answers please!

krek1111 [17]

1) D = 13.6 g / mL

2)ethyl alcohol weighs 158g

3)ρ _copper = 8.9 g $cm^{3}$

Explanation:

1)

D = m / V

=306.0 g / 22.5 mL

D= 13.6 g / mL

2)

density = mass / volume

mass = density × volume

=0.789g /ml × 200.0 ml

M=158g

Ethyl alcohol weighs 158g

3)

ρ (density) = Mass / Volume

ρ _copper = 1896 g / 8.4cm × 5.5cm × 4.6cm

= 1896g / 212.5 $cm^{3}$

ρ _copper=8.9 g $cm^{3}$

4 0

3 years ago