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Questions in chemistry

[Terjawab] Which of these are examples of physical changes? Check all that apply. burning wood freezing water cutting paper iron rusting mixing water and acetone

[Terjawab] An isotope with 15 protons and 17 neutrons will have which symbol? A. ${}_{15}^{17} Cl$ B. ${}_{15}^{17} P$ C. ${}_{17}^{32} Cl$ D. ${}_{17}^{32} P$ E. ${}_{15}^{32} P

[Terjawab] Type the correct answer in the box. Express your answer to three significant figures. The half-life of carbon-14 is 5,730 years. Dating organic material by looking for [tex]$C -14$[/tex] can't be accurately done after 50,000 years. Suppose a fossilized tree branch originally contained 4.30 grams of C-14. How much C-14 would be left after 50,000 years? Use the formula [tex]$N=N_0\left(\frac{1}{2}\right)^{\dagger}$[/tex]. A tree branch that originally had 4.3 grams of carbon-14 will have $\square$ grams after 50,000 years.

[Terjawab] Match the words, definitions, and examples: Element Molecule Compound Mixture Two or more atoms chemically joined together Two or more different atoms chemically joined together A substance made from only one type of atom Different elements, molecules or compounds not chemically joined together

[Terjawab] Complete the table: | Materials found at home | Phase of Matter | Use/s of the material/s at home | |------------------------|-----------------|--------------------------------| | Ex. water | liquid | Use for cooking, washing dishes and clothes, drinking, and taking a bath. | | 1. | | | | 2. | | | | 3. | | | | 4. | | | | 5. | | |

[Terjawab] The value of Z for an atom containing 29 protons, 29 electrons, and 34 neutrons is: A. 58 B. 34 C. 29 D. 63 E. 5

[Terjawab] Calculate the enthalpy of each reaction per mole of reactant using the formula below, which also converts joules to kilojoules. Record to 2 significant figures. [tex]$\Delta H=\frac{-q}{\text { moles }} * \frac{k J}{1000 J}$[/tex] Reaction 1: [ ] kJ/mol Reaction 2: [ ] kJ/mol

[Terjawab] (A) Information about atom of some elements. | Element | Atomic number | No. of elements | No. of neutrons | No. of protons | Mass number | |---|---|---|---|---|---| | P | 7 | | | 7 | | | Q | 12 | | | | | | R | 13 | | | | | | S | 13 | | | | 27 | | T | | 15 | | | 30 | | U | | 18 | | 18 | | (i) Find and write values suitable for the places a, b, c, d, e, f. (ii) What is the element that belongs to group V in 3rd period? (iii) Name 2 isotopes among above elements. (iv) (a) Name the element with the lowest reactivity. (b) What is the reason for the lowest reactivity of that element? (B) Elements react with some other elements under various conditions. Among above elements: (a) Name the element that produces oxide and releases hydrogen gas by reacting with steam. (b) Sometimes after adding this element into hot water with a small amount of phenolphthalein, colourless water turns pink. (i) What is the element added to water? (ii) State whether that element is a metal or non-metal?

[Terjawab] Consider the following intermediate chemical equations: [tex]$\begin{array}{l} 2 Na(s)+Cl 2(g) \rightarrow 2 NaCl(s) \ 2 Na_2 O(s) \rightarrow 4 Na(s)+O_2(g) \end{array}$[/tex] In the final chemical equation, NaCl and [tex]$O _2$[/tex] are the products that are formed through the reaction between [tex]$Na _2 O$[/tex] and [tex]$Cl _2$[/tex]. Before you can add these intermediate chemical equations, you need to alter them by: A. multiplying the second equation by 2. B. multiplying the first equation by 2. C. multiplying the first equation by (1/2). D. multiplying the second equation by (1/4).

[Terjawab] Which statement best explains the change that occurs when gas particles move more slowly? A. The temperature increases because the average kinetic energy decreases. B. The temperature increases because the average kinetic energy increases. C. The temperature decreases because the average kinetic energy decreases. D. The temperature decreases because the average kinetic energy increases.