What mass (in mg) does 2.63 moles of nickel have? 3.56 × 105 mg 1.54 × 105 mg 2.23 × 104 mg 129 mg?

1.54 x 10^5 mg The atomic weight of nickel is 58.6934 Since you have 2.63 moles, the mass will be 2.63 * 58.6934 = 154.3636 grams. Multiply by 1000 to get milligrams 154.3636 * 1000 = 154363.6 g Convert to scientific notation 1.543636 x 10^5 Look at the available options and see what matches. 3.56 x 10^5 mg ; Nope, way too big 1.54 x 10^5 mg; Matches to the number of significant figures given. 2.23 x 10^4 mg; Nope, way too small 129 mg; Nope, way too small.

Yes, endothermic means it turns cold. and some chemical changes include change of tempature.