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san4es73 [151]
3 years ago
13

Instant hot and cold packs are found in many common stores and work when two substances react. Depending on the substances that

react, the reaction either absorbs heat or gives off heat.
The enthalpy of a hot pack is
A. negative
B. positive
C. zero
because the reaction
A. absorbs heat
B. gives off heat
C. does not change temperature
Chemistry
2 answers:
OLga [1]3 years ago
7 0

Answer:

b positive and b gives off heat

Flura [38]3 years ago
3 0

Answer: negative and gives off heat

Explanation:

On edge

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What is the approximate percent by mass of potassium in KHCO3?
lozanna [386]

Answer:

The mass percent of potassium is 39%

Option C is correct

Explanation:

Step 1: Data given

Atomic mass of K = 39.10 g/mol

Atomic mass of H = 1.01 g/mol

Atomic mass of C = 12.01 g/mol

Atomic mass of O = 16.0 g/mol

Step 2: Calculate molar mass of KHCO3

Molar mass KHCO3 = 39.10 + 12.01 + 1.01 + 3*16.0

Molar mass KHCO3 = 100.12 g/mol

Step 3: Calculate mass percent of potassium (K)

%K = (atomic mass of K / molar mass of KHCO3) * 100%

%K = (39.10 / 100.12) * 100%

%K = 39.05 %

The mass percent of potassium is 39%

Option C is correct

8 0
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What is the formula for the compound formed by calcium ions and chloride ions? (1) CaCl (2) CaCl2 (3) CaCl3 (4) Ca2Cl
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I think it would be c
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If the mass of 23 gummi bears is 49.2g, what is the average mass of one gummi bear? Round answer to the nearest 0.00g (do NOT ty
Mila [183]

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A lawnmower runs on gasoline.what type of energy transformation takes place in its engine?
Eva8 [605]
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7 0
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Many monatomic ions are found in seawater, including the ions formed from the following list of elements. Write the Lewis symbol
77julia77 [94]

Answer:

The Lewis structures are in image attached.

Explanation:

Lewis symbol is a representation of an element symbol along with its valence electrons around it in the form of dot(s).

Mono-atomic ions formed from the following :

(a) Cl

Chlorine's atomic number is 17 in which only 7 electrons are present in its valence shell .So in order to gain noble gas stability it will gain 1 electron to completes its octet

Cl=1s^22s^22p^63s^23p^5

Cl^-=1s^22s^22p^63s^23p^6

(b) Na

Sodium's atomic number is 11 in which only 1 electrons are present in its valence shell .So in order to gain noble gas stability it will loose 1 electron to completes its octet. In the Lewis symbol no dot shown as sodium has lost its 1 electron.

Na=1s^22s^23p^63s^1

Na^+=1s^22s^23p^63s^0

(c) Mg

Magnesium's atomic number is 12 in which only 2 electrons are present in its valence shell .So, in order to gain noble gas stability it will loose 2 electrons to completes its octet.

In the Lewis symbol no dot shown as magnesium has lost its 2 electrons.

Mg=1s^22s^23p^63s^2

Mg^{2+}=1s^22s^23p^63s^0

(d)Ca

Calcium's atomic number is 20 in which only 2 electrons are present in its valence shell .So, in order to gain noble gas stability it will loose 2 electron to completes its octet.

In the Lewis symbol no dot shown as calcium has lost its 2 electron.

Ca= 1s^22s^22p^63s^23p^64s^2

Ca^{2+}=1s^22s^23p^6^23p^64s^0

(e) K

Potassium's atomic number is 19 in which only 1 electrons are present in its valence shell .So, in order to gain noble gas stability it will loose 1 electron to completes its octet.

In the Lewis symbol no dot shown as calcium has lost its 1 electron.

K= 1s^22s^22p^63s^23p^64s^1

K^{+}=1s^22s^23p^6^23p^64s^0

(f) Br

Bromine's atomic number is 35 in which only 7 electrons are present in its valence shell .So in order to gain noble gas stability it will gain 1 electron to completes its octet

Br=1s^22s^22p^63s^23p^63d^{10}4s^24p^5

Br^-= 1s^22s^22p^63s^23p^63d^{10}4s^24p^6

(g) Sr

Strontium's atomic number is 38 in which only 2 electrons are present in its valence shell .So, in order to gain noble gas stability it will loose 2 electron to completes its octet.

In the Lewis symbol no dot shown as calcium has lost its 2 electron.

Sr=1s^22s^22p^63s^23p^63d^{10}4s^24p^65s^2

Sr^{2+}=1s^22s^22p^63s^23p^63d^{10}4s^24p^65s^0

(h) F

Florine's atomic number is 7 in which only 7 electrons are present in its valence shell .So in order to gain noble gas stability it will gain 1 electron to completes its octet.

F=1s^22s^22p^5

F^-=1s^22s^22p^6

5 0
3 years ago
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