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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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Many grasses and few trees characterize ____________ (tundras/temperate grasslands).
Oksanka [162]

Answer:

Temperate Grasslands

Explanation:

Tundras have nothing to do with grass. Tundras are more like ice

8 0
3 years ago
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Liquid methanol (CH₃OH) can be used as an alternative fuel in pickup and SUV engines. An industrial method for preparing it invo
r-ruslan [8.4K]

40.6 kJ of heat energy had been emitted.

CO(g) + 2H2(g) CH3OH(l)CO volume, V (CO), equals 15 L or 0.015 m3.

Temperature = 85 0C = 85 + 273 = 358 K Pressure = 112 kPa = 112,000 PaPV = nRT n= 112000 0.015 / 8.314 358 n(CO) = 0.56 moles,

according to the ideal gas law.H2 volume is 14.4 L or 0.0144 m3

T = 750C + 273 K = 348 K n(H2) = 99191.84 0.0144 m3 / 8.314 348 K = 0.49 moles of H2 Pressure = 744 torr = 99191.84 Pa

Hydrogen is the limiting reagent, according to the calculation above.CH3OH = H2 = 0.49/2 = 0.245 m-238.6 (-110.5) = -128.1 kJ/mol for H(rxn) = H(f) (CH3OH) - H (rxn)

We must now multiply H(rxn) by the number of moles of methanol.

E = H(rxn) n(CH3OH) = 128.1 0.245 = 40.6 kJ.

Learn more about Ideal gas law here-

brainly.com/question/13821925

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7 0
2 years ago
Consider the following statements about weeding and identify the incorrect one.
dolphi86 [110]

Answer:

b) Weeding is the process of growing weed

Explanation:

Wedding is an agricultural process carried out to ensure maximum you won't do. It is the process by which weeds i.e. unwanted plants are removed.

As rightly stated in the question;

- Weeding is either done by manual means e.g Cutlasses or use of weedicides, which are chemicals.

- Weeding is best done during tiling operations.

The incorrect option is that "Weeding is the process of growing weed" rather it is a process of removing weed.

4 0
3 years ago
What do you think caused the original properties of the substances to change in order to form “Elephant Toothpaste"?
jarptica [38.1K]
The starting material or materials for a chemical reaction are referred to as the reactants. The substance or substances produced from a chemical reaction are called products. Sometimes a secondary product, a byproduct, can also be created at the same time as the desired product(s).
Not every chemical reaction occurs in the same way. There are different types of chemical reactions, including synthesis reactions, decomposition reactions, and displacement reactions. In this experiment, a decomposition reaction takes place. During a decomposition reaction, a compound breaks apart into two or more products. Most decomposition reactions need an outside source of energy in order to take place.
Hydrogen peroxide is not a very stable compound, so it slowly decomposes into water and oxygen gas under normal conditions. In this reaction, yeast is used as a catalyst. A catalyst is a substance that helps to change the rate of a reaction. During the reaction, the catalyst is not consumed. As a result, the yeast makes the reaction occur much faster; it causes the hydrogen peroxide to break down and release the oxygen gas much faster.
The soap is used to help us “see” the reaction. Bubbles of oxygen become trapped in the soap, creating foam. The reaction occurs so quickly, releasing so much gas and creating so much foam, that the foam begins to flow out of the bottle. The result of this reaction looks like toothpaste being squeezed out of a tube.
In addition, the bottle will feel warm to the touch because the reaction is exothermic. An exothermic reaction or process is one that gives off energy. In contrast, an endothermic reaction or process is one that requires or absorbs energy.
HYPOTHESIS
uAdding yeast to hydrogen peroxide
will cause the hydrogen peroxide to
decompose quickly into water and oxygen gas, creating foam as the gas becomes trapped in liquid dish soap and pushes upward out of the bottle.
FORMULAS & EQUATIONS
Hydrogen peroxide is a relatively clear liquid substance. It is soluble in water and is often sold as a mixture of H2O2 in water. The hydrogen peroxide used in this experiment is actually a 6% solution of H2O2 in water.
The chemical formula for hydrogen peroxide is H2O2.
Hydrogen peroxide naturally decomposes into water and oxygen gas. The reaction is shown by the following equation:
2H2O2 (aq)g2H2O (l) + O2 (g)
The rate of the reaction can be increased by introducing a catalyst. In this experiment, the catalyst is yeast. Yeast is a microorganism that is part of the fungi family. Therefore, in the equation below, the catalyst is indicated above the arrow.
yeast
2H2O2 (aq) g 2H2O (l) + O2 (g)
The hydrogen peroxide used in the experiment is
actually a mixture of water and hydrogen peroxide.
CONNECT TO THE YOU BE THE CHEMIST CHALLENGE
For additional background information, please review CEF’s Challenge study materials online at http://www.chemed.org/ybtc/challenge/study.aspx.
• Additional information on elements, compounds, and physical and chemical changes can be found in the Classification of Matter section of CEF’s Passport to Science Exploration: The Core of Chemistry.
• Additional information on chemical reactions can be found in the Chemical Reactions section of CEF’s Passport to Science Exploration: Chemistry
8 0
3 years ago
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Describe the structure of atoms including locations and changes of protons,neutrons,and electrons
EastWind [94]

Atoms are made up of three basic particles: protons, electrons, and neutrons. Protons and neutrons are found in the nucleus, and the nucleus is found in the very center of an atom. Protons are positively charged whereas neutrons have no charge.

Electrons are found on the electron shells, and the electron shells are found in in the outermost region of an atom. The outermost electron shell contains valence electrons. Electrons are negatively charged.

The number of protons vary depending on the atomic number of an atom. The number of neutrons vary depending on the atomic mass and atomic number of an atom. To find the neutron you must subtract the atomic mass from the atomic number. The number of electrons in a neutral atom also vary depending on the atomic number.

Sorry this is so long. I didn't quite understand your question so I added the last paragraph in just in case it was helpful in any way. I hope I helped!

8 0
3 years ago
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