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2 years ago

Please answer the questions in the pic! 15 points!

Chemistry

1 answer:

lesya [120]2 years ago

3 0

1. 80 Kj
2. 120-80= 40 Kj
3. 120-20= 100Kj
4. 20-80= -60Kj
5. +60 Kj
6. Exothermic because 4 is negative

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Calculate the percent activity of the radioactive isotope strontium-89 remaining after 5 half-lives.

maria [59]

The answer to this question would be: 3.125%

Half-life is the time needed for a radioactive molecule to decay half of its mass. In this case, the strontium-89 is already gone past 5 half lives. Then, the percentage of the mass left after 5 half-lives should be:
100%*(1/2^5)= 100%/32=3..125%

5 0

2 years ago

Calculate the amount of solute needed for 1000 ml of 15% sodium thiosulfate

maksim [4K]

15% = 15 grams of solute in 100 mL solution

15 g --------------- 100 mL
?? ------------------ 1000 mL

1000 x 15 / 100 =

15000 / 100 => 150 g of solute

hope this helps!

7 0

3 years ago

2Mg + O2 → 2MgO<br><br> If you are burning 5.8332 g of Mg, how many grams of MgO will this make?

LekaFEV [45]

<h3>Answer:</h3>

9.6724 g MgO

<h3>General Formulas and Concepts:</h3>

<u>Math</u>

<u>Pre-Algebra</u>

Order of Operations: BPEMDAS

Brackets
Parenthesis
Exponents
Multiplication
Division
Addition
Subtraction

Left to Right

<u>Chemistry</u>

<u>Stoichiometry</u>

Reading a Periodic Table
Using Dimensional Analysis

<h3>Explanation:</h3>

<u>Step 1: Define</u>

[RxN - Balanced] 2Mg + O₂ → 2MgO

[Given] 5.8332 g Mg

<u>Step 2: Identify Conversions</u>

[RxN] 2 mol Mg = 2 mol MgO

Molar Mass of Mg - 24.31 g/mol

Molar Mass of O - 16.00 g/mol

Molar Mass of MgO - 24.31 + 16.00 = 40.31 g/mol

<u>Step 3: Stoichiometry</u>

Set up: $\displaystyle 5.8332 \ g \ Mg(\frac{1 \ mol \ Mg}{24.31 \ g \ Mg})(\frac{2 \ mol \ MgO}{2 \ mol \ Mg})(\frac{40.31 \ g \ MgO}{1 \ mol \ MgO})$
Multiply/Divide: $\displaystyle 9.67241 \ g \ MgO$

<u>Step 4: Check</u>

<em>Follow sig fig rules and round. We are given 5 sig figs.</em>

9.67241 g MgO ≈ 9.6724 g MgO

5 0

2 years ago

Read 2 more answers

Each carbon atom of benzene is involved in two ________

coldgirl [10]

Answer:

Benzene is a combination of carbon and hydrogen atoms. The hybridization is sp2 type. During the hybridization of benzene, each carbon atom forms different bonds with two other similar carbon atoms instead of just one.

hope it helps!

please mark as the brainliest!

7 0

2 years ago

A chemist must dilute of aqueous sodium carbonate solution until the concentration falls to . He'll do this by adding distilled

Mademuasel [1]

The question is incomplete, complete question is :

A chemist must dilute 73.9 mL of 400 mM aqueous sodium carbonate solution until the concentration falls to 125 mM . He'll do this by adding distilled water to the solution until it reaches a certain final volume. Calculate this final volume, in liters. Be sure your answer has the correct number of significant digits.

Answer:

The final volume of the solution will be 0.236 L.

Explanation:

Concentration of sodium carbonate solution before dilution = $M_1= 400 mM$