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3 years ago

Which of the following is evidence of a chemical change?

Chemistry

2 answers:

krek1111 [17]3 years ago

5 0

the formation of a gas

larisa86 [58]3 years ago

5 0

Answer:

the formation of a gas

Explanation:

The chemical change is one in which some chemical reaction occur.

a) Phase change : it is simply change of one state of matter to another.

For example conversion of ice to liquid water, where there is no change in chemical composition of water and only the physical state is changing.

b) formation of gas: it is possible when some substance breaks into some other components or some substance reacts with other. This is definitely a chemical change as bonds will break and may be new bonds will form.

For example decomposition of calcium carbonate gives carbon dioxide (a gas) and calcium oxide.

c) mass change: it could be due to evaporation of water from a substance. Which must be a physical change.

d) surface area: change in surface is area must be due to change in state or physical modifications in state of a substance.

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Read 2 more answers

Select the equations below that represent physical changes.

Ierofanga [76]

Physical changes- any change in the physical properties of the substance is a physical change. Generally physical properties include color, state, size , shape, odour, appearance . In any phyical change, no new substance is formed.

Chemical changes- any change in the chemical properties of the substance is a chemical change. Chemical properties changes only when something new is formed during a reaction.

∴ Part A- 2 H2O(l) → 2 H2(g) + O2(g)

In this, H2 and O2 is produced during the reaction which is different from H20. Thus, it is a chemical change.

Part B- H2O(l) → H2O(s)

In this, only the state of water changes from liquid to solid and no new product is formed. Thus, it is a physical change.

Part C-CO2(s) → CO2(g)

In this also, only the state of CO2 changes from solid to gas and no new product is formed. Thus, it is a physical change.

Part D-H2(g) → 2 H(g)

In this reaction, H2 molecule is dissociated into 2 hydrogen atom leading to formation of new products. Thus, it is a chemical change.

Finally, equations that represent physical changes are - B and C

B. H2O(l) → H2O(s)

C. CO2(s) → CO2(g)

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3 years ago

El fluoruro de hidrógeno HF que se utiliza en

Blizzard [7]

Answer:

25.6g de HF son producidos

Explanation:

...¿Cuánto HF es producido?

Para resolver este problema debemos convertir la masa de cada reactivo a moles usando su masa molar. Como la reacción es 1:1, el reactivo con menor número de moles es el reactivo limitante. Con las moles del reactivo limitante podemos obtener las moles de HF y su masa así:

Moles CaF2:

Masa molar:

1Ca = 40g/mol

2F = 19*2 = 38g/mol

40+38 = 78g/mol

50g CaF2 * (1mol/78g) = 0.641 moles CaF2

Moles H2SO4:

Masa molar:

2H = 2g/mol

1S = 32g/mol

4O = 64g/mol

98g/mol

100g H2SO4 * (1mol / 98g) = 1.02 moles H2SO4

Como las moles de CaF2 < Moles H2SO4: CaF2 es reactivo limitante.

Moles HF usando la reacción:

0.641 moles CaF2 * (2mol HF / 1mol CaF2) = 1.282 moles HF

Masa HF:

Masa molar:

1g/mol + 19g/mol = 20g/mol

1.282 moles HF * (20g/mol) =

<h3>25.6g de HF son producidos</h3>

8 0

2 years ago

Two liquids, 1 and 2, are in equilibrium in a u-tube that is open at both ends. the liquids do not mix, and liquid 1 rests on to

Artyom0805 [142]

I believe the density p1 is greater than the density p2 .
Since the liquid are at equilibrium in the the open U-tube, the pressure at which the liquids meet should be the same. That is at the position where they are in contact, the pressure that liquid 1 exerts at that point is the same as the pressure exerted by liquid 2 at the point.

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2 years ago