Setting of cement is:(A) exothermic reaction (B) endothermic reaction(C) neither endothermic nor exothermic (D) none of these. Answer Verified Hint: Setting is called as the action of changing from a fluid state to a solid state. During setting when water reacts with cement it liberates heat.
Complete step by step answer: So, the correct answer is Option A. Note: Wet cement is strongly corrosive and can cause severe skin burns and even if they come in contact with mucous membranes it can cause severe eye or respiratory irritation.
Cement is known to a binder that is used in construction sites.Depending upon the ability of the cement to set in the presence of water, cement is divided into:(1). Non-hydraulic cement(2). Hydraulic cementNon – hydraulic cement is that which does not set in wet conditions or under water.
- It sets as it dries and reacts with carbon dioxide in the air.
- It does not get attacked by the chemicals after setting.
- Hydraulic cement is that which sets and becomes adhesive due to a reaction with dry ingredients and water.
- Hydraulic cements consist of a mixture of silicates and oxides.
- The process of formation of cement includes the calcination process of limestone that is calcium carbonate.
The reaction of burning of limestone is:$ } }_ }} \to } }_ }}$From this reaction carbon is removed from limestone and the formation of lime occurs. Then, after this lime reacts with silicon dioxide to produce dicalcium silicate and tricalcium silicate.
The reaction can be written as:$ } }_ }} \to } } }_ }} \\ } }_ }} \to } } }_ }} \\ $Then, lime reacts with aluminium oxide to form tricalcium aluminate.$ } }_ }} }_ }} \to } } }_ }} }_ }}$At last, calcium oxide, aluminium oxide and ferric oxide react together to form cement.$ } }_ }} }_ }} } }_ }} }_ }} \to } } }_ }} }_ }} } }_ }} }_ }}$When cement is mixed with water it starts to set and causes hydration chemical reactions.
The hydration of the constituents occurs slowly and the material solidly and hardens.$CaO.A + 6 O \to 3CaO.A,6 O + \operatorname $ During setting and hardening of cement, some amount of heat is liberated due to hydration and the chemical reactions that occur.As the release of heat takes place.
- 1 Is setting of cement physical change?
- 2 What is setting of cement in chemistry?
- 3 Is hardening chemical change?
- 4 What type of change is the setting of cement on coming in contact with water?
Is setting of cement physical change?
Solution : Setting of cement is an example of permanent change which is irreversible, hence is not a physical change.
Is cement a physical property?
Physical Properties of Cement – Different blends of cement used in construction are characterized by their physical properties. Some key parameters control the quality of cement. The physical properties of good cement are based on:
- Fineness of cement
- Setting time
- Heat of hydration
- Loss of ignition
- Bulk density
- Specific gravity (Relative density)
These physical properties are discussed in details in the following segment. Also, you will find the test names associated with these physical properties.
Which change is irreversible *?
Chemical changes are changes that occur in the chemical properties of the substance like its flammability, radioactivity, etc. All chemical changes are irreversible changes. Once the chemical properties of a substance are changed, it becomes another substance. Thus, it cannot return to its original state.
What is irreversible reaction example?
An irreversible reaction is a reaction that proceeds in one direction only; the products do not react together to reform the reactants. An example of this is when the fuel in a Bunsen burner undergoes combustion.
What is setting of cement in chemistry?
What is setting of cement? – When water is mixed with cement, a smooth paste is produced that remains plastic for a short time. During this period, the paste can be disturbed and remixed without injury. As the reaction between water and cement continues, the plasticity of the cement paste is lost. This early period in the hardening of cement is known as ‘Setting of Cement’. Prev Post What are the raw materials used in the manufacturers of Portland cement? Next Post Are there different types of Portland Cement?
Is hardening chemical change?
Key Concepts and Summary – All substances have distinct physical and chemical properties, and may undergo physical or chemical changes. Physical properties, such as hardness and boiling point, and physical changes, such as melting or freezing, do not involve a change in the composition of matter.
Chemical properties, such flammability and acidity, and chemical changes, such as rusting, involve production of matter that differs from that present beforehand. Measurable properties fall into one of two categories. Extensive properties depend on the amount of matter present, for example, the mass of gold.
Intensive properties do not depend on the amount of matter present, for example, the density of gold. Heat is an example of an extensive property, and temperature is an example of an intensive property.
Is hardening a chemical or physical property?
Learning Outcomes –
- Identify properties of and changes in matter as physical or chemical
- Identify properties of matter as extensive or intensive
The characteristics that enable us to distinguish one substance from another are called properties. A physical property is a characteristic of matter that is not associated with a change in its chemical composition. Familiar examples of physical properties include density, color, hardness, melting and boiling points, and electrical conductivity.
We can observe some physical properties, such as density and color, without changing the physical state of the matter observed. Other physical properties, such as the melting temperature of iron or the freezing temperature of water, can only be observed as matter undergoes a physical change. A physical change is a change in the state or properties of matter without any accompanying change in its chemical composition (the identities of the substances contained in the matter).
We observe a physical change when wax melts, when sugar dissolves in coffee, and when steam condenses into liquid water (Figure 1). Other examples of physical changes include magnetizing and demagnetizing metals (as is done with common antitheft security tags) and grinding solids into powders (which can sometimes yield noticeable changes in color). Figure 1. (a) Wax undergoes a physical change when solid wax is heated and forms liquid wax. (b) Steam condensing inside a cooking pot is a physical change, as water vapor is changed into liquid water. (credit a: modification of work by “95jb14″/Wikimedia Commons; credit b: modification of work by “mjneuby”/Flickr) The change of one type of matter into another type (or the inability to change) is a chemical property, Figure 2. (a) One of the chemical properties of iron is that it rusts; (b) one of the chemical properties of chromium is that it does not. (credit a: modification of work by Tony Hisgett; credit b: modification of work by “Atoma”/Wikimedia Commons) A chemical change always produces one or more types of matter that differ from the matter present before the change. Figure 3. (a) Copper and nitric acid undergo a chemical change to form copper nitrate and brown, gaseous nitrogen dioxide. (b) During the combustion of a match, cellulose in the match and oxygen from the air undergo a chemical change to form carbon dioxide and water vapor.
C) Cooking red meat causes a number of chemical changes, including the oxidation of iron in myoglobin that results in the familiar red-to-brown color change. (d) A banana turning brown is a chemical change as new, darker (and less tasty) substances form. (credit b: modification of work by Jeff Turner; credit c: modification of work by Gloria Cabada-Leman; credit d: modification of work by Roberto Verzo) Properties of matter fall into one of two categories.
If the property depends on the amount of matter present, it is an extensive property, The mass and volume of a substance are examples of extensive properties; for instance, a gallon of milk has a larger mass and volume than a cup of milk. The value of an extensive property is directly proportional to the amount of matter in question.
- If the property of a sample of matter does not depend on the amount of matter present, it is an intensive property,
- Temperature is an example of an intensive property.
- If the gallon and cup of milk are each at 20 °C (room temperature), when they are combined, the temperature remains at 20 °C.
- As another example, consider the distinct but related properties of heat and temperature.
A drop of hot cooking oil spattered on your arm causes brief, minor discomfort, whereas a pot of hot oil yields severe burns. Both the drop and the pot of oil are at the same temperature (an intensive property), but the pot clearly contains much more heat (extensive property). Figure 4. The National Fire Protection Agency (NFPA) hazard diamond summarizes the major hazards of a chemical substance. The National Fire Protection Agency (NFPA) 704 Hazard Identification System was developed by NFPA to provide safety information about certain substances.
- The system details flammability, reactivity, health, and other hazards.
- Within the overall diamond symbol, the top (red) diamond specifies the level of fire hazard (temperature range for flash point).
- The blue (left) diamond indicates the level of health hazard.
- The yellow (right) diamond describes reactivity hazards, such as how readily the substance will undergo detonation or a violent chemical change.
The white (bottom) diamond points out special hazards, such as if it is an oxidizer (which allows the substance to burn in the absence of air/oxygen), undergoes an unusual or dangerous reaction with water, is corrosive, acidic, alkaline, a biological hazard, radioactive, and so on.
- Each hazard is rated on a scale from 0 to 4, with 0 being no hazard and 4 being extremely hazardous.
- While many elements differ dramatically in their chemical and physical properties, some elements have similar properties.
- We can identify sets of elements that exhibit common behaviors.
- For example, many elements conduct heat and electricity well, whereas others are poor conductors.
These properties can be used to sort the elements into three classes: metals (elements that conduct well), nonmetals (elements that conduct poorly), and metalloids (elements that have properties of both metals and nonmetals). The periodic table is a table of elements that places elements with similar properties close together (Figure 5). Figure 5. The periodic table shows how elements may be grouped according to certain similar properties. Note the background color denotes whether an element is a metal, metalloid, or nonmetal, whereas the element symbol color indicates whether it is a solid, liquid, or gas.
- All substances have distinct physical and chemical properties, and may undergo physical or chemical changes.
- Physical properties, such as hardness and boiling point, and physical changes, such as melting or freezing, do not involve a change in the composition of matter.
- Chemical properties, such flammability and acidity, and chemical changes, such as rusting, involve production of matter that differs from that present beforehand.
Measurable properties fall into one of two categories. Extensive properties depend on the amount of matter present, for example, the mass of gold. Intensive properties do not depend on the amount of matter present, for example, the density of gold. Heat is an example of an extensive property, and temperature is an example of an intensive property.
- Classify the six underlined properties in the following paragraph as chemical or physical: Fluorine is a pale yellow gas that reacts with most substances. The free element melts at −220 °C and boils at −188 °C. Finely divided metals burn in fluorine with a bright flame. Nineteen grams of fluorine will react with 1.0 gram of hydrogen.
- Classify each of the following changes as physical or chemical:
- condensation of steam
- burning of gasoline
- souring of milk
- dissolving of sugar in water
- melting of gold
- Classify each of the following changes as physical or chemical:
- coal burning
- ice melting
- mixing chocolate syrup with milk
- explosion of a firecracker
- magnetizing of a screwdriver
- The volume of a sample of oxygen gas changed from 10 mL to 11 mL as the temperature changed. Is this a chemical or physical change?
- A 2.0-liter volume of hydrogen gas combined with 1.0 liter of oxygen gas to produce 2.0 liters of water vapor. Does oxygen undergo a chemical or physical change?
- Explain the difference between extensive properties and intensive properties.
- Identify the following properties as either extensive or intensive.
- boiling point
- The density (d) of a substance is an intensive property that is defined as the ratio of its mass (m) to its volume (V).\text =\dfrac } }; \text =\dfrac } }. Considering that mass and volume are both extensive properties, explain why their ratio, density, is intensive.
What type of change is the setting of cement on coming in contact with water?
18.1.2 Cement hydration – The addition of water to OPC powder commences immediately with the cement hydration reactions, These series of chemical reactions result in the subsequent setting and hardening of the cement paste. Needle-like crystals of calcium sulfoaluminate hydrate, namely ettringite, are formed within a few minutes.
- The ettringite subsequently transforms to monosulfate hydrate after a time.
- Two hours after the start of the cementation process, large prismatic crystals of calcium hydroxide (CH) and very small crystals of calcium silicate hydrates (C–S–H) begin to fill the empty pores previously occupied by water and the hydrated cement particles.
Therefore the major components of the hydrated cement paste are: Calcium silicate hydrate : This is the most important hydration product and forms nearly 60% of the volume of solids. It is formed by a layer of sponge-like structures with a large high surface area (~ 500 m 2 /g).
The end product strength is largely contributed by the C–S–H formation and is attributed mainly by their van der Waals physical adhesion forces. Calcium hydroxide : This is the second most abundant component with respect to the volume of solids and constitutes about 25%. It is formed of large plate-like crystals with a smaller surface area compared to C–S–H.
It contributes to limited van der Waal binding forces and is relatively highly soluble compared to C–S–H, and renders the concrete reactive to acidic solutions. Calcium sulfoaluminate : This has a minor role in the cementitious structure properties, and forms almost ~15% of the volume of solids.
|Component||Estimated reaction rate|
|3CaO·SiO 2||Fast relative to 2CaO·SiO 2|
|2CaO·SiO 2||Slow compared to 3CaO·SiO 2|
|3CaO·Al 2 O 3||Fastest, but addition of gypsum retards the rate|
|4CaO·Al 2 O 3 ·Fe 2 O 3||Relatively slow|
|CaSO 4 ·2H 2 O (gypsum)||Retardant|
The approximate hydration reactions between water and the cement components can be represented for each of the Portland cement major ingredient as follows. These equations are not stoichiometrically balanced due to the variations in the products formed and their compositions.
For C 3 S : C 3 S + 6 H 2 O → C 3 S 2,3 H 2 O + 3 Ca ( HO ) 2 For C 2 S : C 2 S + 4 H 2 O → C 3 S 2,3 H 2 O + 3 Ca ( HO ) 2 For C 3 A : C 3 A + 6 H 2 O → C 3 A,6 H 2 O For C 4 AF : 4 C 4 AF + 2 Ca ( OH ) 2 + 10 H 2 O → C 3 A,6 H 2 O + C 3 F,6 H 2 O It is clear that both silicates, C 3 S and C 2 S, need almost the same mass of water for hydration.
However, calcium hydroxide resulting from C 3 S hydration is more than twice that obtained from C 2 S hydration. It is worth stating that the reaction rate of C 3 A is quicker than that of calcium silicates, Read full chapter URL: https://www.sciencedirect.com/science/article/pii/B9780128189610000181