Answer - A substance is matter that has a uniform and definite composition. All samples of substances, sometimes called pure substances, have identical properties.
Answer:
Regional metamorphic rocks form from other rocks (protoliths) by changes in mineralogy and texture in response to changing physical conditions (temperature, lithostatic pressure, and, in most cases, shear stress). Regional metamorphism occurs over broad areas in the lithosphere, possibly influenced by the heat supply. Regional metamorphic rock results from regional metamorphism and usually develops a flaky texture. These changes are essentially solid-state reactions, but very often a fluid phase is present, either participating in the reaction or as a reaction medium. Many regional metamorphic rocks have a chemical composition that is very similar to that of their sedimentary or igneous precursors, with the exception of removal or addition of volatiles (mainly H2O and CO2). This type of behavior is termed isochemical metamorphism. Metamorphism may also take place as a result of a change in chemical environment; this may occur by transport of elements between chemically contrasting rock types (e.g., formation of calc-silicate minerals at a quartzite–marble contact) or by circulation of fluids that dissolve some substances and precipitate others. This process of significant chemical change during metamorphism is known as allo-chemical metamorphism or metasomatism, and rocks formed in this manner are metasomatic rocks. Metasomatism is, however, mostly of local significance, and the total volume of metasomatic rocks in regional metamorphic terranes is rather minor. The distinction between metasomatism and is chemical metamorphism is also a matter of scale. On the scale of individual grains, mass transport takes place during all phase transformations; on the scale of a thin section, it is probably the rule for regional metamorphism; on the scale of a hand (sized) specimen, it can be observed frequently; and on a larger scale, it is the exception.
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Answer:
-21 kJ·mol⁻¹
Explanation:
Data:
H₃O⁺ + OH⁻ ⟶ 2H₂O
V/mL: 50 50
c/mol·dm⁻³: 1.0 1.0
ΔT = 4.5 °C
C = 4.184 J·°C⁻¹g⁻¹
C_cal = 50 J·°C⁻¹
Calculations:
(a) Moles of acid

So, we have 0.050 mol of reaction
(b) Volume of solution
V = 50 dm³ + 50 dm³ = 100 dm³
(c) Mass of solution

(d) Calorimetry
There are three energy flows in this reaction.
q₁ = heat from reaction
q₂ = heat to warm the water
q₃ = heat to warm the calorimeter
q₁ + q₂ + q₃ = 0
nΔH + mCΔT + C_calΔT = 0
0.050ΔH + 100×4.184×4.5 + 50×4.5 = 0
0.050ΔH + 1883 + 225 = 0
0.050ΔH + 2108 = 0
0.050ΔH = -2108
ΔH = -2108/0.0500
= -42 000 J/mol
= -42 kJ/mol
This is the heat of reaction for the formation of 2 mol of water
The heat of reaction for the formation of mol of water is -21 kJ·mol⁻¹.
Answer:
1) atomic number is the same. Both, chlorine atom and anion, have atomic number 17. They have 17 protons in nucleus of an atom.
2) both are the same element.
Explanation:
endothermic means it absorbs energy while exothermic means it releases energy. remember this.