CHEMISTRY HIGH SCHOOL

The element in Period 4 and Group 1 of the Periodic Table would be classified as aA. metal
B. metalloid
C. nonmetal
D. noble gas

Answers

Answer 1
Answer: Option A. Metal

Starting from K- Potassium up to As-Arsenic  are all metals, the three elements are special: Se-Selenium(Non-Metals),Br-Bromine(Halogens),Kr-Noble gas still part of the row but not classified as metal.

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What volume of oxygen at STP is required for the complete combustion of 100.50 mL of C2H2?

Answers

The given substance combusts following the reaction:

C2H2 + (5/2)O2 -> 2CO2 + H2O

Assume C2H2 is an ideal gas. At STP, 1 mol of an ideal gas occupies 22.4 L. Given 100.50 mL of C2H2, this means that there is 4.4866 x 10^(-3) mol. Combusting 1 mol of C2H2 consumes (5/2) mol of O2, then combusting the given amount of C2H2 consumes 0.01121 mol of O2. At STP, this amount of O2 occupies 251.25 mL. 

Answer: 251.25 ml

Explanation: 2C_2H_2(g)+5O_2(g)\rightarrow 4CO_2+2H_2O

According to Avogadro's law, 1 mole of every gas occupies 22.4 L at Standard temperature and pressure (STP).

2 moles of  C_2H_2(g) occupy = 2* 22.4L=44.8L=44,800ml

5 moles of O_2(g) occupy = 5* 22.4L=112L=112000ml

Thus 44800 ml of C_2H_2(g) reacts with 112000 ml of O_2(g) at STP

100.50 ml of C_2H_2(g) reacts with =(112000)/(44800)* 100.50=251.25 ml of O_2(g) at STP.

In terms of energy, how would you classify the following chemical reaction?2Cu + O2 -> 2CuO + 315 kJ
a.endothermic
b.exothermic
c. both endothermic and exothermic
d. neither endothermic nor exothermic
2. The total amount of energy before and after a chemical reaction is the same. Thus, energy is
a. created
b. destroyed
c. conserved
d. the same as mass

Answers

1. Answer;

- Exothermic reaction

Explanation;

-Exothermic reactions are types of chemical reactions in which heat energy is released to the surroundings. Since enthalpy change is the difference between the energy of products an that of reactants. It means that in an exothermic reaction the energy of products is less than that of products. In this case an energy of 315kJ is released to the surroundings.

2. Answer;

Conserved

-The total amount of energy before and after a chemical reaction is the same. Thus, energy is conserved.

Explanation;

-According to the law of conservation of energy, energy is neither created nor destroyed. Energy may change form during a chemical reaction. For example, energy may change form from chemical energy to heat energy when gas burns in a furnace. However, the exact amount of energy remains after the reaction as before, which is true for all chemical reactions.

Answer:

Whole test

D

D

B

C

B

C

Explanation:

Two substances, A and Z, are to be identified. Substance A can not be broken down by a chemical change. Substance Z can be broken down by a chemical change. What can be concluded about these substances?(1) Both substances are elements.
(2) Both substances are compounds.
(3) Substance A is an element and substance Z is a compound.
(4) Substance A is a compound and substance Z is an element.

Answers

Answer;

(3) Substance A is an element and substance Z is a compound.

Explanation;

-A compound is a substance formed when two or more chemical elements are chemically bonded together, such as water, carbon dioxide, methane, etc while an element is a pure chemical substance made of same type of atoms, such includes, oxygen, potassium, hydrogen, carbon, etc.

- Compounds can be brokendown or decomposed into simpler substances: elements cannot be broken down chemically into simpler substances .

The answer is (3) Substance A is an element and Z is a compound. The chemical reaction can only break the chemical bond but can not change the atom. So A will is an element. 

1. What kind of diagram shows how energy flows from one organism to another?a. producer c. consumer
b. ecology d. food chain

Answers

It would be D.the food chain

The total pressure inside a 1.62 cylinder kept at 35°C is 1.15 atm. If the volume of the cylinder drops to 0.74 L and the temperature remains the same, what is the new pressure inside the cylinder?

Answers

By exponential outcome 21934

Which of the following cannot pass across the placenta?(a) oxygen
(b) waste materials
(c) blood
(d) nutrients

Answers

The placenta is the structure that allows for transfer of wastes, oxygen, and
nutrients between the mother and the fetus.  The fetal blood comes extremely
close to the maternal blood in the placenta, but there is no intermingling of fetal
and maternal blood.  The fetus and mother can even have, and often do have,
different blood types.
Oxygen cannot pass through the placenta
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