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3 years ago

Can somebody help me with this question please

Chemistry

1 answer:

Tasya [4]3 years ago

7 0

Answer:

concave lens

Explanation:

it's concave lens because it diverges the ray/beam of light.

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Which of the following pairs of compounds would you expect to form homogeneous solutions when combined? a)CH3CH2CH2CH2CH3 AND CH

Stolb23 [73]

Which of the following pairs of compounds would you expect to form homogeneous solutions when combined?
a) CH3CH2CH2CH2CH3 AND CH3CH2CH2CH2CH2CH3
and
c) LiNO3 and H2O

8 0

3 years ago

Write a balanced equation for the combustion of C7H16(l) (heptane) -- i.e. its reaction with O2(g) forming the products CO2(g) a

JulsSmile [24]

Answer:

The standard enthalpy of reaction = -4854.7kJ

The difference: ΔH-ΔE = Δ(PV) = Δn.R.T = 9910.288 J ≈ 9.91 kJ

Explanation:

The balanced chemical equation for the combustion of heptane:

C₇H₁₆ (l) + 11 O₂ (g) → 7 CO₂ (g) + 8 H₂O (l)

Given: The standard enthalpy of formation ( $\Delta H _{f}^{\circ }$ ) for: C₇H₁₆ (l) = -187.8 kJ/mol, O₂ (g) = 0 kJ/mol, CO₂ (g) = -393.5 kJ/mol, H₂O (l) = -286 kJ/mol

To calculate the standard enthalpy of reaction ( $\Delta H _{r}^{\circ }$ ) can be calculated by the Hess's law:

$\Delta H _{r}^{\circ } = \left [\sum \nu \cdot\Delta H _{f}^{\circ }(products) \right ] - \left [\sum \nu\cdot\Delta H _{f}^{\circ }(reactants) \right ]$

Here, $\nu$ is the stoichiometric coefficient

⇒ $\Delta H _{r}^{\circ } =$

$\left [ 7\times \Delta H _{f}^{\circ }\left (CO_{2}\right )+ 8\times \Delta H _{f}^{\circ }\left (H_{2}O \right )\right ]$

$- \left [1\times \Delta H _{f}^{\circ }\left (C_{7}H_{16}\right ) +11\times \Delta H _{f}^{\circ }\left (O_{2} \right ) \right ]$

$=\left [ 7\times \left (-393.5 kJ/mol \right )+ 8\times \left (-286 kJ/mol \right )\right ]$

$-\left [1\times \left (-187.8 kJ/mol \right ) +11\times \left (0 kJ/mol \right ) \right ]$

⇒ $\Delta H _{r}^{\circ } = \left [ \left (-2754.5 \right )+ \left (-2288 \right )\right ]\left -[ \left (-187.8 \right ) +\left (0 \right )\right ]$

⇒ $\Delta H _{r}^{\circ } = \left [ -5042.5 ]\left -[ -187.8] = \left ( -4854.7kJ \right )$

To calculate the difference: ΔH-ΔE=Δ(PV)

We use the ideal gas equation: P.V = n.R.T

⇒ ΔH-ΔE=Δ(PV) = Δn.R.T

Given: Temperature:T = 298K, R = 8.314 J⋅K⁻¹⋅mol⁻¹

Δn = number of moles of gaseous products - number of moles of gaseous reactants = (7)- (11) = (-4)

⇒ ΔH-ΔE=Δ(PV) = Δn.R.T = (-4 mol) × (8.314 J⋅K⁻¹⋅mol⁻¹) × (298K) = 9910.288 J = 9.91 kJ (∵ 1 kJ = 1000J )

8 0

3 years ago

How many grams of Cl are in 525g of CaCl2

Tema [17]

First we determine the moles CaCl2 present:

525g / (110.9g/mole) = 4.73 moles CaCl2 present

Based on stoichiometry, there are 2 moles of Cl for every mole of CaCl2:
(2moles Cl / 1mole CaCl2) x 4.73 moles CaCl2 = 9.47 moles Cl

Get the mass:
9.47moles Cl x 35.45g/mole = 335.64 g Cl

8 0

3 years ago

. What happens the pH of an acid solution as a base is added?

Dmitrij [34]

As a base is added to an acidic solution, the H+ ions in solution that make it acidic are slowly neutralized into water (via OH-, the base). As these ions are converted into water the concentration of them decreases, so the pH decreases, as they are directly related.

Hope this helps!

3 0

3 years ago

Which of the following happens when chlorine forms an ion?

Jlenok [28]

What happens when chlorine form an ion is that it gains an electron and has an octet in its outer shell ( answer A)

Explanation

Chlorine is is in atomic number 17 in periodic table.

The electron configuration of chlorine is 1S2 2S2 2P6 3S2 3P5 or[Ne]3S2 3p5 or 2.8.7.

chlorine therefore has 7 valence electron therefore it gain 1 electron to form Cl- ( ion)

Cl- has 8 electron in its outer shell ( it obeys octet rule of eight valence in outer shell.

7 0

3 years ago

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